refactor!: Remove "data" event from SafeEventEmitterProvider (#6328)

## Explanation

The `SafeEventEmitterProvider` `'data'` event relies on the
`JsonRpcEngine` `'notification'` event, which per #6327 we are trying to
get rid of. After failing to find an instance outside of tests where we
actually use the `'data'` event, we assess that it can be removed.

## References

* Ref: #6327

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [x] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/contributing.md#updating-changelogs),
highlighting breaking changes as necessary
- [x] I've prepared draft pull requests for clients and consumer
packages to resolve any breaking changes (really just checking that CI
passes in this case)
   - MetaMask/metamask-extension#35498  
   - MetaMask/metamask-mobile#18907

Author: rekmarks

packages/eth-json-rpc-provider/CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- **BREAKING:** Remove `'data'` event ([#6328](https://github.com/MetaMask/core/pull/6328))
+  - This event was forwarding the `'notification'` event from the underlying `JsonRpcEngine`. It was rarely used in practice, and is now removed.
 - Bump `@metamask/utils` from `^11.2.0` to `^11.4.2` ([#6054](https://github.com/MetaMask/core/pull/6054))
 
 ## [4.1.8]

packages/eth-json-rpc-provider/src/safe-event-emitter-provider.test.ts

@@ -35,32 +35,6 @@ function createMockEngine(method: string, response: Json) {
 }
 
 describe('SafeEventEmitterProvider', () => {
-  describe('constructor', () => {
-    it('listens for notifications from provider, emitting them as "data"', async () => {
-      const engine = new JsonRpcEngine();
-      const provider = new SafeEventEmitterProvider({ engine });
-      const notificationListener = jest.fn();
-      provider.on('data', notificationListener);
-
-      // `json-rpc-engine` v6 does not support JSON-RPC notifications directly,
-      // so this is the best way to emulate this behavior.
-      // We should replace this with `await engine.handle(notification)` when we update to v7
-      // TODO: v7 is now integrated; fix this
-      engine.emit('notification', 'test');
-
-      expect(notificationListener).toHaveBeenCalledWith(null, 'test');
-    });
-
-    it('does not throw if engine does not support events', () => {
-      // TODO: Replace `any` with type
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      const engine = new JsonRpcEngine() as any;
-      delete engine.on;
-
-      expect(() => new SafeEventEmitterProvider({ engine })).not.toThrow();
-    });
-  });
-
   it('returns the correct block number with @metamask/eth-query', async () => {
     const provider = new SafeEventEmitterProvider({
       engine: createMockEngine('eth_blockNumber', 42),

packages/eth-json-rpc-provider/src/safe-event-emitter-provider.ts

@@ -64,12 +64,6 @@ export class SafeEventEmitterProvider extends SafeEventEmitter {
   constructor({ engine }: { engine: JsonRpcEngine }) {
     super();
     this.#engine = engine;
-
-    if (engine.on) {
-      engine.on('notification', (message: string) => {
-        this.emit('data', null, message);
-      });
-    }
   }
 
   /**