Enable DropExternalModelStatementTests170 tests

The parser already supports DROP EXTERNAL MODEL statements. This
commit adds the expected ast.json output files and enables both
the base and Baselines170 variants of the test.

Author: claude

parser/testdata/Baselines170_DropExternalModelStatementTests170/ast.json

@@ -0,0 +1,28 @@
+{
+  "$type": "TSqlScript",
+  "Batches": [
+    {
+      "$type": "TSqlBatch",
+      "Statements": [
+        {
+          "$type": "DropExternalModelStatement",
+          "IsIfExists": false,
+          "Name": {
+            "$type": "SchemaObjectName",
+            "BaseIdentifier": {
+              "$type": "Identifier",
+              "QuoteType": "NotQuoted",
+              "Value": "my_model1"
+            },
+            "Count": 1,
+            "Identifiers": [
+              {
+                "$ref": "Identifier"
+              }
+            ]
+          }
+        }
+      ]
+    }
+  ]
+}

parser/testdata/Baselines170_DropExternalModelStatementTests170/metadata.json

@@ -1 +1 @@
-{"skip": true}
+{"skip": false}

parser/testdata/DropExternalModelStatementTests170/ast.json

@@ -0,0 +1,28 @@
+{
+  "$type": "TSqlScript",
+  "Batches": [
+    {
+      "$type": "TSqlBatch",
+      "Statements": [
+        {
+          "$type": "DropExternalModelStatement",
+          "IsIfExists": false,
+          "Name": {
+            "$type": "SchemaObjectName",
+            "BaseIdentifier": {
+              "$type": "Identifier",
+              "QuoteType": "NotQuoted",
+              "Value": "my_model1"
+            },
+            "Count": 1,
+            "Identifiers": [
+              {
+                "$ref": "Identifier"
+              }
+            ]
+          }
+        }
+      ]
+    }
+  ]
+}

parser/testdata/DropExternalModelStatementTests170/metadata.json

@@ -1 +1 @@
-{"skip": true}
+{"skip": false}

skipped_tests_by_size.txt

@@ -1,5 +1,3 @@
-33 Baselines170_DropExternalModelStatementTests170
-33 DropExternalModelStatementTests170
 69 Baselines90_MiscDeprecatedIn100Tests
 95 AlterCreateDatabaseStatementTests90
 98 MiscDeprecatedIn100Tests