sympow: 1.018.1 -> 2.023.4

Maintenance taken over by debian package maintainer jgmbenoit:
https://trac.sagemath.org/ticket/3360#comment:17

This moves sympow to his fork, since there is no offical
version-controlled source repository from the original author and they
do not seem to maintain sympow anymore. We had already accumulated quite
some patches from debian, who have effectively maintained sympow for a
while now.