Fix flakiness in NativeBinderStatsTest

FakeSettingsProvider.clearSettingsProvider() needs to be invoked both
before and after testing, but we were calling it only after testing.

This can have cause the low-rate flakiness of
NativeBinderStatsTest#testSettingsObserver_disabledByDefault.

Bug: 430062908
Bug: 407694522
Test: atest FrameworksCoreTests_Presubmit:com.android.internal.os.NativeBinderStatsTest#testSettingsObserver_disabledByDefault
Flag: EXEMPT fixing a test
Change-Id: I902c044fc6f9e4ac02b017f43bd52a542026ab87