Revert "openal: Grab volume from manager instead of assuming max volume."

This reverts commit 7fb30ae070b1b8a65c5996334153ded33c2ce1f9.

See #64 for discussion.

panda/src/audiotraits/openalAudioSound.cxx

@@ -44,7 +44,7 @@ OpenALAudioSound(OpenALAudioManager* manager,
   _loops_completed(0),
   _source(0),
   _manager(manager),
-  _volume(manager->get_volume()),
+  _volume(1.0f),
   _balance(0),
   _play_rate(1.0),
   _positional(positional),