[ticket/10174] Rename "Ban usernames" to "Ban users" in ACP

Changing the language string from "Ban usernames" to "Ban users"
to clarify its use. It bans users by their name and not the username itself

PHPBB3-10174
Merge remote-tracking branch 'schosser/ticket/10174' into develop-olympus

* schosser/ticket/10174:
  [ticket/10174] Rename "Ban usernames" to "Ban users" in ACP