docs: Removing Android dev docs from Gerrit

Android developer docs are now maintained in Piper, go/dac-source

Removing all files from Gerrit, since these files can cause build
errors if they refer to classes that are later removed (whence
bug b/35849713 ).

Gerrit already has readme files in these directories telling people
docs are not maintained here; these readmes will be a lot easier to
spot now.

Ran a doc build with these files deleted, and it seems to work fine,
so submitting this CL *shouldn't* break anything.

Merged to master to resolve conflict.
Merged-In: Ic74c3f97f9620daf23543930a8b7ed1386f4d172

Bug: 35849713
Change-Id: I5331cdc968be817ff70ba32dd03fce76493a6ab8