Disable compatibility check for framework-doc*-stubs

Previously, the `framework-doc-stubs` and `framework-doc-system-stubs`
used the `check_api.last_released` to provide a previously released API
to which flagged APIs could be reverted but hid any compatibility
issues to avoid having to baseline any incompatibilities in multiple
places.

This change disables the compatibility check altogether instead of just
hiding any issues found.

Flag: EXEMPT build fix to improve flag support
Bug: 425309457
Test: TH
Change-Id: I7f94957ad971a38193241d81c95eb22db4a6988c