Revert "Add back navigation bar customization."

This reverts commit 3d78c928b3cdee7c2bf54c73ed4e8efd02cf8b87.

Conflicts:
	res/xml/system_ui_settings.xml
	src/com/android/settings/Utils.java

Change-Id: Id91eda56f727928f81ed398c7c763f8cc6294da8