Switch gcnodir name from basename to just removing .so

$(basename) was catching all of the hidl services that have versions
like "1.0" in their name, marking the .0-service portion as a suffix to
be removed.

Instead just remove ".so" and assume that everything else isn't actually
a suffix.

Bug: 69271974
Test: NATIVE_COVERAGE=true COVERAGE_PATHS=hardware/interfaces m; compare
      ninja files
Change-Id: I76e27d9ab1f9d4862cc2607c5f2ed9c121879421