Drop the no-op Android.bp.

The "subdirs=" statement no longer has any effect (with the CL in [1]
that's merged last November). All the Android.bp's will be picked up
automatically.

[1] commit 4f21237342e715cbbac6e409cd67e86a304483c4 in
https://android-review.googlesource.com/c/platform/build/blueprint/+/530115.

Test: mmma -j bootable/recovery
Change-Id: Idd39af1fff907e8c1886f91eea0dd4a9e38a4079