cleanup: remove acknowledge method from TextChannel & DMChannel (#3635)

* Update TextChannel.js

* remove acknowledge method

src/structures/DMChannel.js

@@ -83,7 +83,6 @@ class DMChannel extends Channel {
   createMessageCollector() {}
   awaitMessages() {}
   // Doesn't work on DM channels; bulkDelete() {}
-  acknowledge() {}
   _cacheMessage() {}
 }
 

src/structures/TextChannel.js

@@ -138,7 +138,6 @@ class TextChannel extends GuildChannel {
   createMessageCollector() {}
   awaitMessages() {}
   bulkDelete() {}
-  acknowledge() {}
 }
 
 TextBasedChannel.applyToClass(TextChannel, true);