I don't believe we use this anymore. People using it should upgrade to a newer
NDK (or, worst case, download android-cmake themselves).

Change-Id: Ia99d7b19d6f2ec3f4ffe90795813b00480dc2d60
Reviewed-on: https://boringssl-review.googlesource.com/c/34004
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>