manifest: drop the `indexfile` from `manifestrevlog` Since `manifestrevlog` object are not revlog (no really, they are not…) we drop the revlog specific attribute. We need to directly access the underlying revlog in a couple of place that already assume that we have a revlog here. This is motivated by future change to that revlog attribute. Differential Revision: https://phab.mercurial-scm.org/D10572