Delete multitree api imports code

The mutltiree workflow has not been in use for a while. This CL cleans
up the code that was added to support multitree.

Details
- Delete cc_api_library, cc_api_headers, cc_api_variant module types.
  These module types contain build rules for prebuilt stub .so and .h
files
- Update the DepsMutator of cc.Module to not create a dependency on a
  sibling cc_api_* module if it exists. e.g. do not create a dependency
on libfoo.apiimports if libfoo is listed in `shared_libs`.
- Remove cc_api_library from the stub/impl selection logic for cc
  modules

Test: m nothing --no-skip-soong-tests
Test: presbumits
Change-Id: Ie194157fb3bbc630f384cdd9b694b0fba6786ded