mapi: Delete execmem support code.

No longer used now that we don't dynamically generate dispatch stubs.

Acked-by: Marek Olšák <marek.olsak@amd.com>
Acked-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23451>

src/mapi/shared-glapi/meson.build

@@ -22,8 +22,6 @@ files_shared_glapi = files(
   '../entry.c',
   '../u_current.c',
   '../u_current.h',
-  '../u_execmem.c',
-  '../u_execmem.h',
   'glapi.c',
   'stub.c',
   'stub.h',