android: Drop the Android.mk build system

android: Drop the Android.mk build system

Android.mk files haven't really been supported by Mesa devs for a long
time.  Most of us have been willing to update Makefile.sources if we
remember and sometimes we try to blind code some Android.mk for a new
generator.  However, the reality is that it breaks regularly and ends up
being maintained by the Android community.  To address this problem
another approach was implemented in !10183 utilizing the maintained
meson build system.  The old Android.mk files are no longer required.

This commit was created with the following commands:

    git rm **/Android.mk
    git rm **/Android.*.mk
    git rm **/Makefile.sources
    git rm CleanSpec.mk

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/4487
Acked-by: Roman Stratiienko <r.stratiienko@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9728>