histedit-test: drop skip logic for older mercurial version

We are shipped in core now.

tests/test-histedit-revspec.t

@@ -1,7 +1,3 b''
-This test requires parentrevspec support in revsets, so check for that
-and skip the test if we're on an unusual hg that supports .t tests but
-not parentrevspec.
-  $ python -c 'from mercurial import revset ; revset.methods["parentpost"]' || exit 80
 
 Enable extensions used by this test.
   $ cat >>$HGRCPATH <<EOF