Unset Dream overlay component in CTS test.

This changelist ensures the dream overlay component is unset from
the system after the overlay test completes. Leaving this value
set causes the application process to crash in subsequent tests,
which can least to unintended failures.

Test: atest DreamOverlayTest
Bug: 214401991
Change-Id: I7d8873ba35687dddbd4bb470e68087287492a3ac
1 file changed