* Remove the order from RAs, it is now defined in terms of the ⋅ operation.
* Define ownership using the step-indexed order.
* Remove the order also from DRAs and change STS accordingly. While doing
  that, I changed STS to no longer use decidable token sets, which removes the
  requirement of decidable equality on tokens.

Also change the definition of agreement slightly, so agree_map can be defined
for any function, and not just non-expansive functions.

in cofe_maps.v.