Remove resources from SystemUI-tests

The test resources are provided by SystemUI-tests-base, but
SystemUI-tests was implicitly picking up the main SystemUI tests
while using the com.android.systemui.tests Android package.  This
should have shadowed the R classes from SystemUI-tests-base, but the
classpath order of the R classes was backwards.  Remove the implicit
resources from SystemUI-tests to allow swapping the R classpath
order.

Bug: 294256649
Test: m SystemUITests
Flag: NONE
Change-Id: I41ede1c2899994986dc6e265466626f67a2aec46