Remove preference_category_material_settings.xml

This layout was moved to the support library as a part of the work for
b/64689839, so we don't need a copy of it in SettingsLib anymore.

Bug: 110037570
Test: compile (all consumers of SettingsLib should no longer be
referencing this layout)

Change-Id: I084898a35f18427ca15c8e103af34b3e90b9a85e