sound: Remove obsolete DV_F_* flags

The ISA sound drivers that used them are retired.

Last reference of DV_F_DRQ_MASK and DV_F_DUAL_DMA:
716924c ("Retire snd_sbc ISA sound card
driver")

Last reference of DV_F_DEV_MASK and DV_F_DEV_SHIFT:
5126e5e ("Retire snd_mss ISA sound card
driver")

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Reviewed by:	markj, emaste
Differential Revision:	https://reviews.freebsd.org/D44858

sys/dev/sound/pcm/sound.h

@@ -341,14 +341,6 @@ void snd_mtxassert(void *m);
 int sndstat_register(device_t dev, char *str);
 int sndstat_unregister(device_t dev);
 
-/* usage of flags in device config entry (config file) */
-#define DV_F_DRQ_MASK	0x00000007	/* mask for secondary drq */
-#define	DV_F_DUAL_DMA	0x00000010	/* set to use secondary dma channel */
-
-/* ought to be made obsolete but still used by mss */
-#define	DV_F_DEV_MASK	0x0000ff00	/* force device type/class */
-#define	DV_F_DEV_SHIFT	8		/* force device type/class */
-
 /*
  * this is rather kludgey- we need to duplicate these struct def'ns from sound.c
  * so that the macro versions of pcm_{,un}lock can dereference them.