Ignore 'cmd font clear' failure in tearDown().

This would fail (as expected) on Pixel 3 / 3a.
On Pixel 3 / 3a, we skip the test in assumeTrue() in setUp(). tearDown()
should not throw and make the test fail.

Bug: 187364676
Test: forrest
Change-Id: I9e82c2e27c3ef71e73bf022db543318cfc0f2ef7