un-document 'resolve_path' API endpoint

to avoid publishing it on 5/24 since we want to change its
semantics somewhat

test plan: the "Resolve path" endpoint should no longer
appear in the Files API documentation

refs CNVS-13260

Change-Id: I52525eced1c879d57da6a7adadcde177496f3ac7
Reviewed-on: https://gerrit.instructure.com/35355
Reviewed-by: Ryan Shaw <ryan@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>