gnu: Remove python-potr.

The last release of the package dates from 2018.
According to its self-description: "This software is experimental and
potentially insecure. Do not rely on it"
It depends on the cryptography library python-pycrypto, which has had
its last release in 2013 and "is unmaintained, obsolete, and contains
security vulnerabilities" according to its homepage.

* gnu/packages/python-crypto.scm (python-potr): Delete variable.

gnu/packages/python-crypto.scm

@@ -75,30 +75,6 @@
   #:use-module ((guix licenses) #:prefix license:)
   #:use-module (srfi srfi-1))
 
-(define-public python-potr
-  (package
-    (name "python-potr")
-    (version "1.0.2")
-    (source
-     (origin
-       (method git-fetch)
-       (uri
-        (git-reference
-         (url "https://github.com/python-otr/pure-python-otr")
-         (commit version)))
-       (file-name
-        (git-file-name name version))
-       (sha256
-        (base32 "1hzw6h01fm216nmipyylgz0zybd80w1xsk12m7djycnhqrnrvvv1"))))
-    (build-system python-build-system)
-    (propagated-inputs
-     (list python-pycrypto))
-    (synopsis "Python OTR Implementation")
-    (description "Python OTR is an Off-The-Record Protocol Implementation in
-Python.  It does not bind to libotr.")
-    (home-page "https://github.com/python-otr/pure-python-otr")
-    (license license:lgpl3+)))
-
 (define-public python-base58
   (package
     (name "python-base58")