No real changes, just get rid of a variable in wxOSX wxSound code.

Don't define a variable which is used exactly once, testing for the async flag
directly is just as, or even more, readable and shorter.

(this is a backport of 605149ed07 from master)

src/osx/core/sound.cpp

@@ -108,13 +108,11 @@ bool wxOSXAudioToolboxSoundData::Play(unsigned flags)
 
     AudioServicesAddSystemSoundCompletion( m_soundID, CFRunLoopGetCurrent(), NULL, wxOSXAudioToolboxSoundData::CompletionCallback, (void *) this );
 
-    bool sync = !(flags & wxSOUND_ASYNC);
-
     m_playing = true;
 
     AudioServicesPlaySystemSound(m_soundID);
 
-    if ( sync )
+    if ( !(flags & wxSOUND_ASYNC) )
     {
         while ( m_playing )
         {