AF: Reduce redundancy in filtering tests.

resetFilterTest tests some behaviors already tested in testFilter.
Moves checks for filtering on deleting characters into testFilter so
that each test has a clearer purpose.

Bug: 158274878
Test: atest CtsAutoFillServiceTestCases:DatasetFilteringInlineTest \
 CtsAutoFillServiceTestCases:DatasetFilteringDropdownTest
Change-Id: I09afcb798b92fc71a2833b5a7580afc162a5ece4
1 file changed