upgrade: move `printrequirements()` to UpgradeOperation class
Part of refactor where we make things more arranged and integrated into single
`UpgradeOperation` class.
Differential Revision: https://phab.mercurial-scm.org/D9577
$ LANG=nonexistent LC_ALL=nonexistent LANGUAGE=nonexistent hg version -q
Mercurial Distributed SCM (version *) (glob)