Remove broken test

Makes the internal state of MediaOutputController invalid by setting
a non nullable field to null.

Added in ag/19905995 with the likely purpose of covering an
if (mLocalMediaManager == null) that was removed downstream,
causing the test to break in master.

Bug: 248604980
Change-Id: I3ad7acfa6a7e11d272691e96d42f9de3d5dfd16e
Test: N/A. Removing test.