Settings: Only show clear button when search field has text.

Change-Id: I69bf6a31a933459be2c652434aec412105395dcc
Cleanup.

Now that button and keyboard backlight don't use the HW framework
anymore, there's no point in having an abstraction for a single use case.

Change-Id: Ib66b2a29a105d53e3ba4273abb06977b132c1fc8