Remove unused Android.mk under device/google/contexthub am: 2c51922b31

Original change: https://android-review.googlesource.com/c/device/google/contexthub/+/3093623

Change-Id: I59e00ce10d2893faadf6b97cc44219678a179619
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>