recovery: More refactoring of WearUI

This patch performs the following modifications:
- Remove setBackground function, and currentIcon member variable.
- Remove common Progress*, Redraw and EndMenu functions.

Bug: 27407422
Change-Id: Ic3c0e16b67941484c3bc1d04c9b61288e8896808
Signed-off-by: Prashant Malani <pmalani@google.com>