remove deprecated string from untranslated.xml

tools/untranslated.xml

@@ -8,5 +8,4 @@
     <string name="a11y_voice_message_hint_ios">After recording double-tap to send. To discard the recording scrub left-right with two fingers.</string>
     <string name="login_error_no_internet_connection">No internet connection, can\'t log in to your server.</string>
     <string name="share_account_not_configured">Account is not configured.</string>
-    <string name="chat_gallery_empty_state">"No media items in this chat."</string>
 </resources>