Remove remaining references to the footer refactor.

- Remove TODO for isOnEmptySpace (this is only used when scene container
  is off, so it will be removed as part of that refactor)
- Update the way we inject the FooterViewModel to use the recommended
  factory
- Make sure we only create one instance of the viewModel and reuse it;
do the same for the empty shade view model while we're at it

Bug: 293167744
Test: builds
Flag: EXEMPT trivial dagger change
Change-Id: Iaa75b68a3d95d3d0a624f0e59d0d5faf95d5bdfd