stack: remove unnecessary reverse() predicate
Stack already sorts revisions, so no need to do it twice.
This change was a part of D2400, which didn't land for other reasons. See also
D2399, where this change was suggested.
Differential Revision: https://phab.mercurial-scm.org/D6706
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}