Revert "Do not install tethering in TEST_MAPPING"

This reverts commit 33634a02.

Reason for revert:
Tethering was removed from test mapping during S development in some
branches, but is now usable gain in test mapping and needs to be part
of mainline-test-mapping testing.

Change-Id: I6c6e1ffe6d9f6cee68d3e13d548b9c81ae8bf67a
Ignore-AOSP-First: Fixes difference with AOSP
Bug: 196755836
Test: TEST_MAPPING needs to be tested by treehugger