Remove OMX

The API has been abandoned for some time now and there are no more users.
FFmpeg only supports encoding, but it never worked with Mesa.
GStreamer completely removed OMX support in 1.24 release.

Acked-by: Leo Liu <leo.liu@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30865>

meson_options.txt

@@ -118,22 +118,6 @@ option(
   description : 'path to put vdpau libraries. defaults to $libdir/vdpau.'
 )
 
-option(
-  'gallium-omx',
-  type : 'combo',
-  value : 'auto',
-  choices : ['auto', 'disabled', 'bellagio', 'tizonia'],
-  description : 'enable gallium omx frontend.',
-)
-
-option(
-  'omx-libs-path',
-  type : 'string',
-  value : '',
-  description : 'path to put omx libraries. defaults to omx-bellagio ' +
-                'pkg-config pluginsdir.'
-)
-
 option(
   'gallium-va',
   type : 'feature',