cruft-report: Refactor to improve looping over dicts

This commit aims to pre-empty some of the 2to3 delta while also
using more concise constructs.

Examples include:

   y = x.keys()
   y.sort(...)

is rewritten into:

   y = sorted(x.keys(), ...)

(Except in one case, where we really wanted "max" rather than "sort".)

Signed-off-by: Niels Thykier <niels@thykier.net>