Change Android-specific customizations that get preserved.

* Don't preserve README.android. There were only 3 instances of this, 2
  of which were out of date and can be deleted. The last one can be
  replaced with a patch file.
* Treat the android/ directory as a customization, because maintaining
  these as patch files is an unnecessary burden on maintainers. These
  are typically used in the case of *-sys crates and contain build rules
  for building the underlying C library using the source in the Android
  tree.

Bug: http://b/339424309
Test: treehugger
Change-Id: I5a77055fec7531b319315e5641e3d780acc29e3b
1 file changed