refactor(Client): remove fetchAllMembers option (#5257)

* feat(Client): remove fetchAllMembers option & logic

* Cleanup

* Missed type change

src/util/Constants.js

@@ -18,8 +18,6 @@ const { Error, RangeError } = require('../errors');
  * sweepable (in seconds, 0 for forever)
  * @property {number} [messageSweepInterval=0] How frequently to remove messages from the cache that are older than
  * the message cache lifetime (in seconds, 0 for never)
- * @property {boolean} [fetchAllMembers=false] Whether to cache all guild members and users upon startup, as well as
- * upon joining a guild (should be avoided whenever possible)
  * @property {MessageMentionOptions} [allowedMentions] Default value for {@link MessageOptions#allowedMentions}
  * @property {PartialType[]} [partials] Structures allowed to be partial. This means events can be emitted even when
  * they're missing all the data for a particular structure. See the "Partials" topic listed in the sidebar for some
@@ -41,7 +39,6 @@ exports.DefaultOptions = {
   messageCacheMaxSize: 200,
   messageCacheLifetime: 0,
   messageSweepInterval: 0,
-  fetchAllMembers: false,
   partials: [],
   restWsBridgeTimeout: 5000,
   restRequestTimeout: 15000,