Remove the ActivityThread#currentApplication()

ActivityThread#currentApplication() is hidden, so if we want to get the
application context, we can use Context#getApplicationContext() instead.

Bug: 145945457
Test: Manual Test
Change-Id: If67eccda6d016d9140f66e14541c397efbe94d45
Merged-in: If67eccda6d016d9140f66e14541c397efbe94d45
(cherry picked from commit 21f88853)