Remove combined_apis_defaults module type

This change removes the combined_apis_defaults module type, given that
combined_apis module type is not defaultable as it creates a default
module in its module factory. The only usage of this module type has
been removed with https://r.android.com/3184819 .

Test: m nothing --no-skip-soong-tests
Bug: 349800749
Change-Id: Ib78eb965124b2c80e871b1bc022011843ebaab9a