grep: reuse getrenamedfn() from scmutil My motivation is to reduce uses of filectx.renamed(). Reusing scmutil.getrenamedfn() also means that we get some caching of copy information per file and revision. I don't think that matters for `hg grep` (I doubt it speeds up significantly, and I doubt it wastes significant memory), but I'm not sure. Differential Revision: https://phab.mercurial-scm.org/D6022