pcm.4: remove reference to snd_audiocs(4)

The latter has been removed in 58aa35d429
and r357455 respectively.

share/man/man4/pcm.4

@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd May 5, 2020
+.Dd December 26, 2020
 .Dt SOUND 4
 .Os
 .Sh NAME
@@ -706,7 +706,6 @@ A device node is not created properly.
 .Xr snd_ai2s 4 ,
 .Xr snd_als4000 4 ,
 .Xr snd_atiixp 4 ,
-.Xr snd_audiocs 4 ,
 .Xr snd_cmi 4 ,
 .Xr snd_cs4281 4 ,
 .Xr snd_csa 4 ,