Remove fontmgr_android_ndk from Android.bp

This target should not be built into the framework.

Change-Id: Ia59da2aa5ad235b5ff0f6f8ca59e7a72146cc05b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1050156
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Noelle Scobie <nscobie@google.com>