Remove android.test.{mock,runner}.stubs from private-list.txt

Generation of the full list of non-SDK APIs resolves public API
stubs against the boot class path. Remove stubs which do not
correspond to libraries on the boot class path.

This removes "Unresolved" warnings while building the API lists.

Bug: 112002105
Bug: 79409988
Test: m out/target/common/obj/PACKAGING/hiddenapi-private-list.txt
Change-Id: I1a73ed9ee50affed5284692e829a433ec1484f01