This removes the `STRIP_DUPE_UNIQUE_NAME` and `STRIP_DUPE_ALL` macros
and replaces them with an `enum StripDuplicate`.
A flag with a value of 0 was implicitly used as "duplicate selected strips" so the
enum uses `Selected = 0` to document this behavior better.
Pull Request: https://projects.blender.org/blender/blender/pulls/144125