sage.combinat.finite_state_machine: Remove use of "var" #34217
Description
It should use SR.symbol() instead.
We also remove some unnecessary uses of SR and mark some doctests # optional - sage.symbolic (for #32601).
Component: combinatorics
Author: Matthias Koeppe
Branch/Commit: 6e49510
Reviewer: Travis Scrimshaw
Issue created by migration from https://trac.sagemath.org/ticket/34217