Simplify OSS test by removing OpenBSD specific location of the soundcard.h header

OpenBSD has long since stopped using OSS. Remove checking for OpenBSD specific header.

src/audio/dsp/SDL_dspaudio.c

@@ -34,13 +34,7 @@
 #include <sys/ioctl.h>
 #include <sys/stat.h>
 
-#if SDL_AUDIO_DRIVER_OSS_SOUNDCARD_H
-/* This is installed on some systems */
-#include <soundcard.h>
-#else
-/* This is recommended by OSS */
 #include <sys/soundcard.h>
-#endif
 
 #include "SDL_timer.h"
 #include "SDL_audio.h"