Remove unused NSSL#mActivityStarter

The ActivityStarter was used in the NSSL to wire in clicks on the
EmptyShadeView. This has moved to a view binder now.

Bug: 308596826
Test: atest NotificationStackScrollLayoutTest
Flag: EXEMPT refactor

Change-Id: I201b780ebf6a5b2e4fd812aeb567d6cbe48ac28b
2 files changed