android: simplify building libgallium_dri on Android

The versioned libgallium library can be confusing on Android, and it is
probably not even needed there, so simplify the build on Android by
always build the unversioned `libgallium_dri.so` overriding the
`-Dunversion-libgallium=true` option added in
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30579

Remove also all the bits that deal with the versioned library which are
not needed anymore.

Fixes: 9568976c52 ("android: fix build in multiple ways")
Acked-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Mauro Rossi <issor.oruam@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30641>

src/gallium/targets/dri/meson.build

@@ -22,7 +22,7 @@ if with_ld_dynamic_list
   gallium_dri_link_depends += files('../dri.dyn')
 endif
 
-if get_option('unversion-libgallium')
+if get_option('unversion-libgallium') or with_platform_android
   libgallium_name = 'gallium_dri'
 else
   libgallium_name = 'gallium-@0@'.format(meson.project_version())