docs: remove sound API duplication

The sound API is documented on two different parts:
under Documentation/driver-api/sound.rst and under
Documentation/sound/kernel-api/alsa-driver-api.rst.

The alsa-driver-api.rst seems more complete, and APIs
are split per type. There's just one missing kernel-doc
markup there.

Add it and drop the duplicated one.
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/driver-api/index.rst

@@ -27,7 +27,6 @@ available subsections can be seen below.
    component
    message-based
    infiniband
-   sound
    frame-buffer
    regulator
    iio/index

Documentation/driver-api/sound.rst

-Sound Devices
-=============
-
-.. kernel-doc:: include/sound/core.h
-   :internal:
-
-.. kernel-doc:: sound/sound_core.c
-   :export:
-
-.. kernel-doc:: include/sound/pcm.h
-   :internal:
-
-.. kernel-doc:: sound/core/pcm.c
-   :export:
-
-.. kernel-doc:: sound/core/device.c
-   :export:
-
-.. kernel-doc:: sound/core/info.c
-   :export:
-
-.. kernel-doc:: sound/core/rawmidi.c
-   :export:
-
-.. kernel-doc:: sound/core/sound.c
-   :export:
-
-.. kernel-doc:: sound/core/memory.c
-   :export:
-
-.. kernel-doc:: sound/core/pcm_memory.c
-   :export:
-
-.. kernel-doc:: sound/core/init.c
-   :export:
-
-.. kernel-doc:: sound/core/isadma.c
-   :export:
-
-.. kernel-doc:: sound/core/control.c
-   :export:
-
-.. kernel-doc:: sound/core/pcm_lib.c
-   :export:
-
-.. kernel-doc:: sound/core/hwdep.c
-   :export:
-
-.. kernel-doc:: sound/core/pcm_native.c
-   :export:
-
-.. kernel-doc:: sound/core/memalloc.c
-   :export:
-

Documentation/sound/kernel-api/alsa-driver-api.rst

@@ -132,3 +132,4 @@ ISA DMA Helpers
 Other Helper Macros
 -------------------
 .. kernel-doc:: include/sound/core.h
+.. kernel-doc:: sound/sound_core.c