Fix ChooserActivity check for still-alive ChooserTargets

Only prune ChooserTargets if the resolved activity source they came
from is still present after refreshing the list. Compare this directly
against the ComponentName rather than ResolveInfo.equals, as the
latter isn't implemented.

Bug 21953672

Change-Id: I6486bda85c19d7371167affe2a2b80a2668bd734