EventEmitter: Deprecate removeSubscription

Summary:
Deprecates `EventEmitter#removeSubscription`. This required temporarily introducing a new `__removeSubscription` method that is only invoked by `EmitterSubscription`. This is necessary so that we do not completely break usages of `EventEmitter` that are supplying constructor arguments (which is also deprecated, but still supported until the next release).

Calling this method will now cause a warning to appear with instructions to instead invoke `remove()` on the subscription itself.

Lastly, changed `console.error` deprecation notice to instead use `console.warn`. This is in line with the principle that errors are "broken today" and warnings will be "broken tomorrow".

Changelog:
[General][Deprecated] - `EventEmitter#removeSubscription` is now deprecated.

Reviewed By: rubennorte

Differential Revision: D27704279

fbshipit-source-id: 581f5b2ab46b1bcfc1d20898b3d3392988dccbd5

Libraries/vendor/emitter/_EmitterSubscription.js

@@ -54,7 +54,7 @@ class EmitterSubscription<EventDefinitions: {...}, K: $Keys<EventDefinitions>>
  * for removing the subscription lies with the EventEmitter.
  */
  remove(): void {
- this.emitter.removeSubscription(this);
+ this.emitter.__removeSubscription(this);
  }
 }
 

Libraries/vendor/emitter/_EventEmitter.js

@@ -82,6 +82,19 @@ class EventEmitter<EventDefinitions: {...}> {
  */
  removeSubscription<K: $Keys<EventDefinitions>>(
  subscription: EmitterSubscription<EventDefinitions, K>,
+ ): void {
+ console.warn(
+ 'EventEmitter.removeSubscription(...): Method has been deprecated. ' +
+ 'Please instead use `remove()` on the subscription itself.',
+ );
+ this.__removeSubscription(subscription);
+ }
+
+ /**
+ * Called by `EmitterSubscription` to bypass the above deprecation warning.
+ */
+ __removeSubscription<K: $Keys<EventDefinitions>>(
+ subscription: EmitterSubscription<EventDefinitions, K>,
  ): void {
  invariant(
  subscription.emitter === this,
@@ -147,7 +160,7 @@ class EventEmitter<EventDefinitions: {...}> {
  // FIXME: listeners should return void instead of mixed to prevent issues
  listener: (...$ElementType<EventDefinitions, K>) => mixed,
  ): void {
- console.error(
+ console.warn(
  `EventEmitter.removeListener('${eventType}', ...): Method has been ` +
  'deprecated. Please instead use `remove()` on the subscription ' +
  'returned by `EventEmitter.addListener`.',