validations: drop superfluous return statements.

Returning true or false in a validation callback doesn't do anything, so
drop these superfluous return statements.

app/models/user_name_change_request.rb

@@ -64,9 +64,6 @@ class UserNameChangeRequest < ApplicationRecord
   def not_limited
     if UserNameChangeRequest.where("user_id = ? and created_at >= ?", CurrentUser.user.id, 1.week.ago).exists?
       errors.add(:base, "You can only submit one name change request per week")
-      return false
-    else
-      return true
     end
   end