Fix or remove pickling support for Match lists with pybind11

In Swig `MatchList` objects are (un)pickled by creating a `Catalog` of the contained `Record` type and the (un)pickling that.
With pybind11 this is not possible because `MatchList` is just a Python `list` of `Match` objects. Pickling them individually (via the same route) does not make much sense.
It is unclear if this pickling support is actually needed anywhere outside of testSourceMatch.py where it is currently disabled (as of DM-8415).
This ticket aims to either fix or permanently remove this functionality when the need for it becomes clear.