Deprecate Conduit method "diffusion.getrecentcommitsbypath"

Summary:
See D19558. This method has no callers and just wraps diffusion.historyquery, since D5960 (2013).

This was introduced in D315 (which didn't make it out of FB, I think) inside Facebook for unclear purposes in 2011.

Test Plan: Grepped for callers, found none.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: artms

Differential Revision: https://secure.phabricator.com/D19559