Remove busy-work. (#2072)
Remove busy-work. (#2072)

It is entirely sufficient to walk the MRO of the exception class, no need to check for classes re-appearing later on, no need to add the MRO of any superclass.

* Python refuses point-blank to create a class with a circular MRO.
* All classes in a superclass MRO *already* appear in the MRO of the derived type. Re-adding the contents of a superclass MRO is doing double work.
auready/flask,drewja/flask,fkazimierczak/flask,drewja/flask,mitsuhiko/flask,mitsuhiko/flask,tristanfisher/flask,drewja/flask,dawran6/flask,fkazimierczak/flask,pallets/flask,dawran6/flask,auready/flask,pallets/flask,pallets/flask,fkazimierczak/flask,tristanfisher/flask