[ExtractorUnitTest] Fix linker failures with upstream lld

Bug: http://b/197965342

This change is needed to build this test with upstream lld.

Avoid linking static libraries that are already needed by shared_lib
dependencies of ExtractorUnitTest (e.g. libmedia.so).
- Use shared libstagefright and libstagefright_foundation instead.
- libstagefright_mpeg2extractor does not have a shared variant but it
seems unnecessary to link this test.

Test: build with aosp/1809741 which has lld with the above behavior.
Change-Id: Id83e6446a3bf903c891367de8ea2b23bc57efa34