vndk-def: Hide system-to-vendor deps instead

This commit replaces remove_dep() with hide_dep() so that the
dependencies can be kept in deps-insight command.

Before this commit, system-to-vendor dependencies will be removed and
won't be present in the output of deps-insight command.

Test: ./tests/test_vndk.py
Test: ./tests/test_command_deps_insight.py
Change-Id: I377a81f98a726219e241e79ae6274e9b124de035