hg: backout optimizing for treemanifests
It turns out that the files list is not sufficient to identify with revlogs have
changed. In a merge commit, no files could've changed but directories would
have. For now let's just backout this optimization.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
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commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).