gnu: Remove python-msgpack-transitional.

This package is obsolete and unused.

* gnu/packages/python-xyz.scm (python-msgpack-transitional): Remove variable.

gnu/packages/python-xyz.scm

@@ -10846,37 +10846,6 @@ (define-public python-msgpack
     (home-page "https://pypi.org/project/msgpack/")
     (license license:asl2.0)))
 
-;; This msgpack library's name changed from "python-msgpack" to "msgpack" with
-;; release 0.5. Some packages like borg still call it by the old name for now.
-;; <https://bugs.gnu.org/30662>
-(define-public python-msgpack-transitional
-  (package
-    (inherit python-msgpack)
-    (name "python-msgpack-transitional")
-    (version "0.5.6")
-    (source (origin
-              (method url-fetch)
-              (uri (pypi-uri "msgpack" version))
-              (sha256
-               (base32
-                "1hz2dba1nvvn52afg34liijsm7kn65cmn06dl0xbwld6bb4cis0f"))))
-    (arguments
-     (substitute-keyword-arguments (package-arguments python-msgpack)
-       ((#:phases phases)
-        `(modify-phases ,phases
-           (add-after 'unpack 'configure-transitional
-             (lambda _
-               ;; Keep using the old name.
-               (substitute* "setup.py"
-                 (("TRANSITIONAL = False")
-                   "TRANSITIONAL = 1"))
-               ;; This old version is not compatible with Python 3.9
-               (substitute* '("test/test_buffer.py" "test/test_extension.py")
-                 ((".tostring\\(") ".tobytes("))
-               (substitute* '("test/test_buffer.py" "test/test_extension.py")
-                 ((".fromstring\\(") ".frombytes("))
-               #t))))))))
-
 (define-public python2-msgpack
   (package-with-python2 python-msgpack))