Convert to androidx.test from android-support-test.

android-support-test has long been deprecated and unsupported,
and it causes problems having both androidx.test and
androiud.support.test included in one binary.

Bug: 172570181
Test: m -j NullHomeTest mediatunertest mediatranscodingtest mediaroutertest mediaframeworktest BluetoothMidiTests
Change-Id: If86f5634beab88db07656f743b19beddd9d77984