player: remove all rpi-specific code

vo_rpi and its related code has pretty much historically been a
disaster in mpv. The build regularly gets broken and since nobody uses
it, it takes months for anyone to notice. There was also that time where
fullscreen was broken for about a year and a half. Also building in waf
was entirely broken for about a couple of years or so due to mysterious
reasons no one ever figured out (meson magically fixed it).

Anyways, once again the build is broken due to rpi being forgotten about
again, but instead of pretending to support this crap. Just drop it all.
Nowadays, mmal hwdec is a relic since these devices are better off using
the v4l2m2m ffmpeg fork instead which actually uses KMS properly. RPI 1
and 2 probably can't do this and will remain broken but oh well blame
Broadcom for being special snowflakes and not using standard APIs (my
rockpro worked out of the box; just saying). RPI 2 is nearly 10 years
old anyways, so I think you can afford a new SBC by now. If we were
nicer, there would be a deprecation period, but this is broken in the
last major release anyway so too late.

Closes #13402.

meson.build

@@ -1219,16 +1219,7 @@ if plain_gl.allowed()
     features += {'gl': true}
 endif
 
-rpi = dependency('/opt/vc/lib/pkgconfig/brcmegl.pc', 'brcmegl', required: get_option('rpi'))
-features += {'rpi': gl_allowed and rpi.found()}
-if features['rpi']
-    dependencies += rpi
-    features += {'gl': true}
-    sources += files('video/out/opengl/context_rpi.c')
-endif
-
-features += {'egl-helpers': features['egl'] or egl_android.found() or
-             egl_angle_win32.allowed() or features['rpi']}
+features += {'egl-helpers': features['egl'] or egl_android.found() or egl_angle_win32.allowed()}
 if features['egl-helpers']
     sources += files('video/out/opengl/egl_helpers.c')
 endif
@@ -1377,18 +1368,6 @@ if features['ios-gl']
     sources += files('video/out/hwdec/hwdec_ios_gl.m')
 endif
 
-rpi_mmal_opt = get_option('rpi-mmal').require(
-    features['rpi'],
-    error_message: 'rpi was not found!',
-)
-rpi_mmal = dependency('/opt/vc/lib/pkgconfig/mmal.pc', 'mmal', required: rpi_mmal_opt)
-features += {'rpi-mmal': rpi_mmal.found()}
-if features['rpi-mmal']
-    dependencies += rpi_mmal
-    sources += files('video/out/opengl/hwdec_rpi.c',
-                     'video/out/vo_rpi.c')
-endif
-
 libva = dependency('libva', version: '>= 1.1.0', required: get_option('vaapi'))
 
 vaapi_drm = dependency('libva-drm', version: '>= 1.1.0',