Force refactor flag disabled in some unittests

BubblesTest and CentralSurfacesImplTest use the old implementation
explicitly as a dependency, so they fail if the refactor flag is
enabled.

This should fix the presubmit failure in ag/25426992, allowing the flag
to advance to STAGING.

Long-term, I plan to update these tests to check the flag and create the
old or new implementation, but short-term, forcing it disabled is easier
and won't hurt test coverage, so I'm doing it first.

While I'm here, now that I know SysuiTestCase creates a SetFlagsRule,
stop creating my own redundant one in the refactor's own tests.

Bug: 261728888
Test: atest BubblesTest CentralSurfacesImplTest
Test: atest NotificationInterruptStateProviderWrapperTest
Test: atest VisualInterruptionDecisionProviderImplTest
Flag: ACONFIG com.android.systemui.visual_interruptions_refactor DEVELOPMENT
Change-Id: I22afb5c8e6e263b5000cc2e256d4a16fe9806b44