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>

docs/install.rst

@@ -104,15 +104,7 @@ information
 3. Building with AOSP (Android)
 -------------------------------
 
-Currently one can build Mesa for Android as part of the AOSP project,
-yet your experience might vary.
-
-In order to achieve that one should update their local manifest to point
-to the upstream repo, set the appropriate BOARD_GPU_DRIVERS and build
-the libGLES_mesa library.
-
-FINISHME: Improve on the instructions add references to Rob H
-repos/Jenkins, Android-x86 and/or other resources.
+<TODO>
 
 4. Library Information
 ----------------------