Retire Emulator's keyboard from frameworks/base

it is added to the vendor partition.

Bug: 212639052
Test: press the assist button, check that keyboard
Test: events are delivered to the guest (`adb shell getevent -lt`)
Test: and the asistant window appears.
Change-Id: I1b836b975df2fc46383b3f83a6276936874bfea9
Signed-off-by: Roman Kiryanov <rkir@google.com>