Clean up legacy code in lockscreen controller/view model

After a recent refactor (ag/33448654), some of the functions are not
needed anymore and can be removed. This CL also clean up some old code
within this area.

Bug: None
Test: LockscreenSmartspaceControllerTest, LockscreenContentViewModelTest
Flag: EXEMPT clean up
Change-Id: I3e410fed46f600cc778e959a9bf5edf2d4a43c97