Use MAX_VOLUME constant in vlc_telnet (#48491)

We also don't need to call `int()` anymore due to underlying fixes in
the python-vlc-telnet library.

I believe this is the last item extracted from PR #44776.

homeassistant/components/vlc_telnet/media_player.py

@@ -126,7 +126,7 @@ def update(self):
 
             if status:
                 if "volume" in status:
-                    self._volume = int(status["volume"]) / 500.0
+                    self._volume = status["volume"] / MAX_VOLUME
                 else:
                     self._volume = None
                 if "state" in status: