Remove useless Android.mk am: 698c90103a

Original change: https://android-review.googlesource.com/c/platform/external/exoplayer/+/2984452

Change-Id: I3f9fed4655136efc7f9247fece13e46d1698e0d6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>