python: get rid of msgpack-python, fixes #48864

We already have msgpack, which is the same. Building a Python env with
`spacy` resulted in a collision between an `.so` provided through both
`msgpack` and `msgpack-python`.

I don't know why `transitional = True` was set. These kind of things
should be documented!

pkgs/development/python-modules/thinc/default.nix

@@ -8,7 +8,7 @@
 , cymem
 , darwin
 , msgpack-numpy
-, msgpack-python
+, msgpack
 , preshed
 , numpy
 , murmurhash
@@ -44,7 +44,7 @@ buildPythonPackage rec {
    cython
    cymem
    msgpack-numpy
-   msgpack-python
+   msgpack
    preshed
    numpy
    murmurhash