media_addon_server: Don't set the gain at each start

* Fixes the forgotten gain setting issue for startup
sounds.

src/servers/media_addon/MediaFilePlayer.cpp

@@ -100,7 +100,6 @@ MediaFilePlayer::MediaFilePlayer(const char* media_type,
 	if (fInitCheck != B_OK)
 		return;
 
-	fSoundPlayer->SetVolume(1.0f);
 	fSoundPlayer->SetHasData(true);
 	fSoundPlayer->Start();
 }