check-flagged-apis: skip self-referential interfaces

The return value of ClassItem.allInterfaces will sometimes include the
interface itself (e.g.
android.accessibilityservice.BrailleDisplayController). It is unclear
when this happens; it doesn't happen for the unit test.

Update the logic to record the interfaces for a class to filter out
interfaces named the same as the class.

Bug: 334870672
Test: atest --host check-flagged-apis-test
Test: croot && ./build/tools/check-flagged-apis/check-flagged-apis.sh
Change-Id: I8d93c230dfedde30e8d43fefd560a47944085d3a