feat(MessageReaction): add remove method and Client#messageReactionRemoveEmoji (#3723)

* Add support for MessageReaction#remove and MESSAGE_REACTION_REMOVE_EMOJI

* Remove reaction from cache

Co-Authored-By: matthewfripp <50251454+matthewfripp@users.noreply.github.com>

* fix: message may be partial

* Clarify what the event entails

* Document client in MessageReaction

Co-Authored-By: SpaceEEC <spaceeec@yahoo.com>

* await the REST call

* Add MessageReaction#remove to typings

Co-authored-by: matthewfripp <50251454+matthewfripp@users.noreply.github.com>
Co-authored-by: SpaceEEC <spaceeec@yahoo.com>

src/client/actions/MessageReactionRemoveEmoji.js

@@ -0,0 +1,28 @@
+'use strict';
+
+const Action = require('./Action');
+const { Events } = require('../../util/Constants');
+
+class MessageReactionRemoveEmoji extends Action {
+  handle(data) {
+    const channel = this.getChannel(data);
+    if (!channel || channel.type === 'voice') return false;
+
+    const message = this.getMessage(data, channel);
+    if (!message) return false;
+
+    const reaction = this.getReaction(data, message);
+    if (!reaction) return false;
+    if (!message.partial) message.reactions.delete(reaction.emoji.id || reaction.emoji.name);
+
+    /**
+     * Emitted when a bot removes an emoji reaction from a cached message.
+     * @event Client#messageReactionRemoveEmoji
+     * @param {MessageReaction} reaction The reaction that was removed
+     */
+    this.client.emit(Events.MESSAGE_REACTION_REMOVE_EMOJI, reaction);
+    return { reaction };
+  }
+}
+
+module.exports = MessageReactionRemoveEmoji;