refactor: remove user bot methods (#2559)

* [WIP] Remove user bots

* more backend userbot removal

* Add mfaEnabled back

* revert client presences store removal

* partially revert getAuth changes

* remove more no longer used children of ClientUserGuildSettings

* fix a bug with this pr and TextBasedChannel.applyToClass

* remove a syncGuilds reference

* more user bot data handling

* various guildSync cleanup

* bots can't call logout

Had the user/bot portions of the code mixed up. Though, does this need to be a promise anymore?

* make ClientManager#destroy() sync

It nolonger needs to be a promise, and nothing depended on it being a promise that I can tell.

* requested change

* Fix massive error

* no longer used as it's userbot only

src/errors/Messages.js

@@ -6,8 +6,6 @@ const Messages = {
   TOKEN_INVALID: 'An invalid token was provided.',
   TOKEN_MISSING: 'Request to use token, but token was unavailable to the client.',
 
-  FEATURE_USER_ONLY: 'Only user accounts are able to make use of this feature.',
-
   WS_CONNECTION_TIMEOUT: 'The connection to the gateway timed out.',
   WS_CONNECTION_EXISTS: 'There is already an existing WebSocket connection.',
   WS_NOT_OPEN: (data = 'data') => `Websocket not open to send ${data}`,