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/cachy/default.nix

@@ -1,7 +1,7 @@
 { lib, buildPythonPackage, fetchPypi
 , redis
 , memcached
-, msgpack-python
+, msgpack
 }:
 
 buildPythonPackage rec {
@@ -16,7 +16,7 @@ buildPythonPackage rec {
   propagatedBuildInputs = [
     redis
     memcached
-    msgpack-python
+    msgpack
   ];
 
   # The Pypi tarball doesn't include tests, and the GitHub source isn't