Removed the SDL_PATH_DSP environment variable from the NetBSD and OSS audio driver

The AUDIODEV environment variable is no longer used by other audio drivers, and can be used exclusively to specify the DSP audio device.

src/audio/SDL_audiodev.c

@@ -87,10 +87,7 @@ static void SDL_EnumUnixAudioDevices_Internal(const SDL_bool recording, const SD
     }
 
     // Figure out what our audio device is
-    audiodev = SDL_getenv("SDL_PATH_DSP");
-    if (!audiodev) {
-        audiodev = SDL_getenv("AUDIODEV");
-    }
+    audiodev = SDL_getenv("AUDIODEV");
     if (!audiodev) {
         if (classic) {
             audiodev = SDL_PATH_DEV_AUDIO;