Clean up EmptyShade- and FooterViewModel

Just some minor cleanups since I'll be making some changes to these for
b/388472403. Includes updating the tests to use the newer kosmos
utilities and removing an unused field.

Bug: 388472403
Flag: EXEMPT minor cleanup
Test: existing tests pass
Change-Id: Icd7be2ea055a29e3c65cad11fc732d2838c08a3a