gnu: python-mysqlclient: Don't depend on MySQL.

* gnu/packages/databases.scm (python-mysqlclient)[native-inputs]: Move MARIADB
from here to ...
[inputs]: ... here.  Remove MYSQL.

gnu/packages/databases.scm

@@ -2617,12 +2617,11 @@ database).")
          "0kv4a1icwdav8jpl7qvnr931lw5h3v22ids6lwq6qpi1hjzf33pz"))))
     (build-system python-build-system)
     (native-inputs
-     `(("mariadb" ,mariadb)
-       ("nose" ,python-nose)
+     `(("nose" ,python-nose)
        ("mock" ,python-mock)
        ("py.test" ,python-pytest)))
     (inputs
-     `(("mysql" ,mysql)
+     `(("mysql" ,mariadb)
        ("libz" ,zlib)
        ("openssl" ,openssl)))
     (home-page "https://github.com/PyMySQL/mysqlclient-python")