Remove the warning when a context being released is globally current

Just about every implementation allows this, and there's no direct harm caused
by it. However, leave the warnings for when it's still current on specific
threads, as this can cause issues.

Alc/ALc.c

@@ -1458,10 +1458,7 @@ static void ReleaseContext(ALCcontext *context, ALCdevice *device)
     }
 
     if(CompExchangePtr((XchgPtr*)&GlobalContext, context, NULL))
-    {
-        WARN("%p released while current\n", context);
         ALCcontext_DecRef(context);
-    }
 
     LockDevice(device);
     tmp_ctx = &device->ContextList;