output: removed audio_output.sameInAndOutFormats

Eliminate sameInAndOutFormats and check with audio_format_equals()
each time it this information is needed.  Another 4 bytes saved.

src/output_init.c

@@ -86,7 +86,6 @@ int audio_output_init(struct audio_output *ao, ConfigParam * param)
 	ao->plugin = plugin;
 	ao->open = 0;
 
-	ao->sameInAndOutFormats = 0;
 	ao->convBuffer = NULL;
 	ao->convBufferLen = 0;