recovery: Begin refactor of WearUI to use ScreenRecoveryUI

This is the first of a series of changes which move WearUI to subclass
ScreenRecoveryUI, to take advantage of several functions which are
common between the two recovery UI implementations, and already defined
in ScreenRecoveryUI.

This patch changes the base class of WearUI, removes redundant
header includes, and also removes a common function.

Bug: 27407422

Change-Id: I8fd90826900f69272a82e23bd099790e8004d511