transcoding: statically link libmediatranscoding.so in tests

Otherwise test doesn't work after service moved to apex.

bug: 173627260
bug: 159172726
test:
With local changes to move service to apex,
atest TranscodingSessionController_tests
Should not see link error in test.

Change-Id: I4729cb5ee1635a8143fb803b22a20e3c59ce378c