Remove os/Android.mk

Removed the os/Android.mk, and re-writed it in the
build/make/core/tasks/cts.mk (please check the other CL in the same
topic).

Bug: 194402596
Test: m cts-platform-version-check (with the other CL in the same topic)
Test: TreeHugger
Change-Id: I7d018d2b38ab1d9c16e8f08b35214033edd3e910
Merged-In: I7d018d2b38ab1d9c16e8f08b35214033edd3e910
1 file changed