Remove slow automorphism test
Created by: femtobit
As discussed in #620.
This should not significantly affect coverage as .automorphisms()
is also used as part of the graph symmetry tests.
Also, the removed test was essentially comparing one NetworkX method to another framework (and not actually running correctly for a long time while Lattice
s were missing edges). It would make sense to add an automorphism test back if we ever implement this method without relying on NetworkX.