fixit upgrade makes incomplete fix, second run results in metadata error

[amyreese]

from fixit import CstLintRule

class FooRule(CstLintRule):
    ...

Traceback (most recent call last):
  File ../fixit/upgrade/remove_rule_suffix.py", line 58, in visit_ClassDef
    qname = metadata.pop().name
KeyError: 'pop from an empty set'

[zsol]

Hmm, metadata should never be mutated