Remove PEP 621 project.optional-dependencies from Requires-Dist in METADATA,...

Now that flit is updates to version 3.3 and support PEP 621, storage of project metadata in pyproject.toml, it adds project.optional-dependencies into the Requires-Dist in METADATA. This is typically the dependencies needed to build documentation or to run tests. As is, these end up being pulled into the binary dependencies of the package, which is not a good idea. This propose merge removes those items from the project metadata before it gets written out to METADATA.

I've tested this building packages with no non-optional dependencies and also with required dependencies and it seems to work fine. Unless maintainers have disabled dh-python dependency guessing, these get picked up automatically and so it would be nice to get this resolved in unstable quickly so we don't end up with too many packages with unneeded depends.