chore!: Remove deprecated setUsername method (#36831)

Author: MartinSchoeler

.changeset/slimy-hairs-wink.md

@@ -0,0 +1,6 @@
+---
+"@rocket.chat/meteor": major
+---
+
+Removes the deprecated setUsername method
+

apps/meteor/app/lib/server/index.ts

@@ -42,7 +42,6 @@ import './methods/sendSMTPTestEmail';
 import './methods/setAdminStatus';
 import './methods/setEmail';
 import './methods/setRealName';
-import './methods/setUsername';
 import './methods/unarchiveRoom';
 import './methods/unblockUser';
 import './methods/updateMessage';