[DevTools] Remove experimental __IS_INTERNAL_MCP_BUILD__ flag and related code (facebook#35755)

This is unused.

DiffTrain build for [8374c2a](facebook@8374c2a)

Author: shtefanovsock

compiled-rn/VERSION_NATIVE_FB

@@ -1 +1 @@
-19.2.0-native-fb-5063b328-20250815
+19.3.0-native-fb-8374c2ab-20260211

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/react-dom/cjs/ReactDOM-dev.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<90a8d185d9cef24ff667513ed992553c>>
+ * @generated SignedSource<<79dc955d9d37448788d75cd3686a0ab3>>
  */
 
 "use strict";
@@ -20,25 +20,30 @@ __DEV__ &&
     function createPortal$1(children, containerInfo, implementation) {
       var key =
         3 < arguments.length && void 0 !== arguments[3] ? arguments[3] : null;
-      try {
-        testStringCoercion(key);
-        var JSCompiler_inline_result = !1;
-      } catch (e) {
-        JSCompiler_inline_result = !0;
+      if (null == key) key = null;
+      else if (key === REACT_OPTIMISTIC_KEY) key = REACT_OPTIMISTIC_KEY;
+      else {
+        try {
+          testStringCoercion(key);
+          var JSCompiler_inline_result = !1;
+        } catch (e) {
+          JSCompiler_inline_result = !0;
+        }
+        JSCompiler_inline_result &&
+          (console.error(
+            "The provided key is an unsupported type %s. This value must be coerced to a string before using it here.",
+            ("function" === typeof Symbol &&
+              Symbol.toStringTag &&
+              key[Symbol.toStringTag]) ||
+              key.constructor.name ||
+              "Object"
+          ),
+          testStringCoercion(key));
+        key = "" + key;
       }
-      JSCompiler_inline_result &&
-        (console.error(
-          "The provided key is an unsupported type %s. This value must be coerced to a string before using it here.",
-          ("function" === typeof Symbol &&
-            Symbol.toStringTag &&
-            key[Symbol.toStringTag]) ||
-            key.constructor.name ||
-            "Object"
-        ),
-        testStringCoercion(key));
       return {
         $$typeof: REACT_PORTAL_TYPE,
-        key: null == key ? null : "" + key,
+        key: key,
         children: children,
         containerInfo: containerInfo,
         implementation: implementation
@@ -100,6 +105,7 @@ __DEV__ &&
         findDOMNode: null
       },
       REACT_PORTAL_TYPE = Symbol.for("react.portal"),
+      REACT_OPTIMISTIC_KEY = Symbol.for("react.optimistic_key"),
       ReactSharedInternals =
         React.__CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE;
     ("function" === typeof Map &&
@@ -404,5 +410,5 @@ __DEV__ &&
     exports.useFormStatus = function () {
       return resolveDispatcher().useHostTransitionStatus();
     };
-    exports.version = "19.2.0-native-fb-5063b328-20250815";
+    exports.version = "19.3.0-native-fb-8374c2ab-20260211";
   })();

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/react-dom/cjs/ReactDOM-prod.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<55fbd0c70773881b975d20fd0ffb23bf>>
+ * @generated SignedSource<<ba1aa768527d322799f05a1867ad29be>>
  */
 
 "use strict";
@@ -45,13 +45,19 @@ var Internals = {
     p: 0,
     findDOMNode: null
   },
-  REACT_PORTAL_TYPE = Symbol.for("react.portal");
+  REACT_PORTAL_TYPE = Symbol.for("react.portal"),
+  REACT_OPTIMISTIC_KEY = Symbol.for("react.optimistic_key");
 function createPortal$1(children, containerInfo, implementation) {
   var key =
     3 < arguments.length && void 0 !== arguments[3] ? arguments[3] : null;
   return {
     $$typeof: REACT_PORTAL_TYPE,
-    key: null == key ? null : "" + key,
+    key:
+      null == key
+        ? null
+        : key === REACT_OPTIMISTIC_KEY
+          ? REACT_OPTIMISTIC_KEY
+          : "" + key,
     children: children,
     containerInfo: containerInfo,
     implementation: implementation
@@ -203,4 +209,4 @@ exports.useFormState = function (action, initialState, permalink) {
 exports.useFormStatus = function () {
   return ReactSharedInternals.H.useHostTransitionStatus();
 };
-exports.version = "19.2.0-native-fb-5063b328-20250815";
+exports.version = "19.3.0-native-fb-8374c2ab-20260211";

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/react-dom/cjs/ReactDOM-profiling.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<55fbd0c70773881b975d20fd0ffb23bf>>
+ * @generated SignedSource<<ba1aa768527d322799f05a1867ad29be>>
  */
 
 "use strict";
@@ -45,13 +45,19 @@ var Internals = {
     p: 0,
     findDOMNode: null
   },
-  REACT_PORTAL_TYPE = Symbol.for("react.portal");
+  REACT_PORTAL_TYPE = Symbol.for("react.portal"),
+  REACT_OPTIMISTIC_KEY = Symbol.for("react.optimistic_key");
 function createPortal$1(children, containerInfo, implementation) {
   var key =
     3 < arguments.length && void 0 !== arguments[3] ? arguments[3] : null;
   return {
     $$typeof: REACT_PORTAL_TYPE,
-    key: null == key ? null : "" + key,
+    key:
+      null == key
+        ? null
+        : key === REACT_OPTIMISTIC_KEY
+          ? REACT_OPTIMISTIC_KEY
+          : "" + key,
     children: children,
     containerInfo: containerInfo,
     implementation: implementation
@@ -203,4 +209,4 @@ exports.useFormState = function (action, initialState, permalink) {
 exports.useFormStatus = function () {
   return ReactSharedInternals.H.useHostTransitionStatus();
 };
-exports.version = "19.2.0-native-fb-5063b328-20250815";
+exports.version = "19.3.0-native-fb-8374c2ab-20260211";