Remove global state from vendor public libraries

Remove the global list of vendor public library modules used to rewrite
dependencies from the vendor module to the stubs for system modules,
and replace it with building the stubs directly in the system variant
of the vendor module.

Bug: 178231622
Test: vendor_public_library_test.go
Change-Id: I826e69ffd507d7e85fa3d4d85b5157428c642143