histedit-test: drop skip logic for older mercurial version

We are shipped in core now.

tests/test-histedit-revspec.t

@@ -1,69 +1,65 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
   > [extensions]
   > graphlog=
   > histedit=
   > EOF
 
 Repo setup.
   $ hg init foo
   $ cd foo
   $ echo alpha >> alpha
   $ hg addr
   adding alpha
   $ hg ci -m one
   $ echo alpha >> alpha
   $ hg ci -m two
   $ echo alpha >> alpha
   $ hg ci -m three
   $ echo alpha >> alpha
   $ hg ci -m four
   $ echo alpha >> alpha
   $ hg ci -m five
 
   $ hg log --style compact --graph
   @  4[tip]   08d98a8350f3   1970-01-01 00:00 +0000   test
   |    five
   |
   o  3   c8e68270e35a   1970-01-01 00:00 +0000   test
   |    four
   |
   o  2   eb57da33312f   1970-01-01 00:00 +0000   test
   |    three
   |
   o  1   579e40513370   1970-01-01 00:00 +0000   test
   |    two
   |
   o  0   6058cbb6cfd7   1970-01-01 00:00 +0000   test
        one
   
 
 Run a dummy edit to make sure we get tip^^ correctly via revsingle.
   $ HGEDITOR=cat hg histedit "tip^^"
   pick eb57da33312f 2 three
   pick c8e68270e35a 3 four
   pick 08d98a8350f3 4 five
   
   # Edit history between eb57da33312f and 08d98a8350f3
   #
   # Commands:
   #  p, pick = use commit
   #  e, edit = use commit, but stop for amending
   #  f, fold = use commit, but fold into previous commit (combines N and N-1)
   #  d, drop = remove commit from history
   #  m, mess = edit message without changing commit content
   #
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
 
 Run on a revision not ancestors of the current working directory.
 
   $ hg up 2
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg histedit -r 4
   abort: 08d98a8350f3 is not an ancestor of working directory
   [255]