fix(rustdeskserver): remove redundant else with undefined RELEASE variable

The check_for_gh_release function already prints its own 'No update
available' message when the app is up to date. The else block using
${RELEASE} was redundant and caused an empty version string to be shown
(e.g. 'already at v').

Fixes: #14267

ct/rustdeskserver.sh

@@ -48,8 +48,6 @@ function update_script() {
     msg_ok "Services started"
 
     msg_ok "Updated successfully!"
-  else
-    msg_ok "No update required. ${APP} is already at v${RELEASE}"
   fi
   exit
 }