chore!: Remove web worker execution service and environment (#3371)

This is a redo of #3357, which was reverted in #3359 to avoid two
breaking changes in a row. Now that #3322 is merged, we can do this
again.

The original PR description can be found below.

---

This removes the web worker execution service and execution environment,
as they were unused. We can revert this PR in the future to add them
again, if needed.

## Breaking changes

### `@metamask/snaps-controllers`

- Remove web worker execution service.

### `@metamask/snaps-execution-environments`

- Remove web worker pool execution environment.
- Remove web worker executor execution environment.

Author: Mrtenz

packages/snaps-controllers/coverage.json

@@ -1,6 +1,6 @@
 {
-  "branches": 93.54,
-  "functions": 97.38,
-  "lines": 98.34,
-  "statements": 98.08
+  "branches": 93.51,
+  "functions": 97.36,
+  "lines": 98.33,
+  "statements": 98.17
 }

packages/snaps-controllers/src/services/browser.test.ts

@@ -6,7 +6,6 @@ describe('browser entrypoint', () => {
     'setupMultiplex',
     'IframeExecutionService',
     'OffscreenExecutionService',
-    'WebWorkerExecutionService',
     'ProxyPostMessageStream',
     'WebViewExecutionService',
     'WebViewMessageStream',

packages/snaps-controllers/src/services/browser.ts

@@ -5,4 +5,3 @@ export * from './ProxyPostMessageStream';
 export * from './iframe';
 export * from './offscreen';
 export * from './webview';
-export { WebWorkerExecutionService } from './webworker';

packages/snaps-controllers/src/services/index.ts

@@ -3,4 +3,3 @@ export type * from './ExecutionService';
 export * from './ProxyPostMessageStream';
 export * from './iframe';
 export * from './offscreen';
-export { WebWorkerExecutionService } from './webworker';