CODEX_MODULE_DIR is always the /modules subdirectory of
CODEX_LIBRARY_DIR, so remove it and derive it that way instead.
- Update tests accordingly
- Rename test data files accordingly
- Use CODEX_LIBRARY_DIR in one place where we had neglected to use a
constant
Change-Id: Ieb347c2d128f3addfb11f6aca79d63969434f342