Remove Subscribable.Mixin from React Native core

Summary: There are no longer any callsites to this in React Native so we can remove it from the repo!

Reviewed By: RSNara

Differential Revision: D10316313

fbshipit-source-id: bd63c823c56bb1914e4249d972e0ce503aa189f8

Libraries/Components/Subscribable.js

@@ -1,65 +0,0 @@
-/**
- * Copyright (c) Facebook, Inc. and its affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *
- * @format
- * @flow
- */
-
-'use strict';
-
-import type EventEmitter from 'EventEmitter';
-
-/**
- * Subscribable provides a mixin for safely subscribing a component to an
- * eventEmitter
- *
- * This will be replaced with the observe interface that will be coming soon to
- * React Core
- */
-
-const Subscribable = {};
-
-Subscribable.Mixin = {
-  UNSAFE_componentWillMount: function() {
-    this._subscribableSubscriptions = [];
-  },
-
-  componentWillUnmount: function() {
-    // This null check is a fix for a broken version of uglify-es. Should be deleted eventually
-    // https://github.com/facebook/react-native/issues/17348
-    this._subscribableSubscriptions &&
-      this._subscribableSubscriptions.forEach(subscription =>
-        subscription.remove(),
-      );
-    this._subscribableSubscriptions = null;
-  },
-
-  /**
-   * Special form of calling `addListener` that *guarantees* that a
-   * subscription *must* be tied to a component instance, and therefore will
-   * be cleaned up when the component is unmounted. It is impossible to create
-   * the subscription and pass it in - this method must be the one to create
-   * the subscription and therefore can guarantee it is retained in a way that
-   * will be cleaned up.
-   *
-   * @param {EventEmitter} eventEmitter emitter to subscribe to.
-   * @param {string} eventType Type of event to listen to.
-   * @param {function} listener Function to invoke when event occurs.
-   * @param {object} context Object to use as listener context.
-   */
-  addListenerOn: function(
-    eventEmitter: EventEmitter,
-    eventType: string,
-    listener: Function,
-    context: Object,
-  ) {
-    this._subscribableSubscriptions.push(
-      eventEmitter.addListener(eventType, listener, context),
-    );
-  },
-};
-
-module.exports = Subscribable;