Watcher backends: remove unused event types

Summary:
Currently watcher backends, which extend `EventEmitter`, emit two events for any file change:
 - One with event name `change`/`add`/`delete`
 - One with event name `all`, and `change`/`add`/`delete` in the payload.

We only ever listen to `all`. The former type is neither exercised nor tested. This removes the unused events.

Changelog: Internal

Reviewed By: hoxyq

Differential Revision: D67393484

fbshipit-source-id: 9ef824710be5f88f8e7d5462e37b076fe5aa0847

packages/metro-file-map/src/watchers/FSEventsWatcher.js

@@ -194,7 +194,6 @@ export default class FSEventsWatcher extends EventEmitter {
     file: string,
     metadata?: ChangeEventMetadata,
   ) {
-    this.emit(type, file, this.root, metadata);
     this.emit(ALL_EVENT, type, file, this.root, metadata);
   }
 

packages/metro-file-map/src/watchers/NodeWatcher.js

@@ -395,7 +395,6 @@ module.exports = class NodeWatcher extends EventEmitter {
     file: string,
     metadata: ?ChangeEventMetadata,
   ) {
-    this.emit(eventType, file, this.root, metadata);
     this.emit(ALL_EVENT, eventType, file, this.root, metadata);
   }
 

packages/metro-file-map/src/watchers/WatchmanWatcher.js

@@ -308,7 +308,6 @@ export default class WatchmanWatcher extends EventEmitter {
     root: string,
     changeMetadata?: ChangeEventMetadata,
   ) {
-    this.emit(eventType, filepath, root, changeMetadata);
     this.emit(ALL_EVENT, eventType, filepath, root, changeMetadata);
   }