hidden: remove _consistencyblockers()

hidden: remove  _consistencyblockers()

Roughly speaking, we currently do this to reveal hidden ancestors of
visible revisions:

 1. Iterate over all visible non-public revisions and see if they have
    hidden parents

 2. For each revision found in step (1) walk the chain of hidden
    commits and reveal it

We can simplify that by skipping step (1) and doing step (2) from all
visible non-public revisions instead.

This doesn't seem to have much impact on "perfvolatilesets".

Before:
! obsolete
! wall 0.004616 comb 0.000000 user 0.000000 sys 0.000000 (best of 570)
! visible
! wall 0.008235 comb 0.010000 user 0.010000 sys 0.000000 (best of 326)

After:
! obsolete
! wall 0.004727 comb 0.010000 user 0.010000 sys 0.000000 (best of 543)
! visible
! wall 0.008371 comb 0.000000 user 0.000000 sys 0.000000 (best of 324)

--- a/mercurial/repoview.py	Sat May 27 22:43:37 2017 -0700
+++ b/mercurial/repoview.py	Sat May 27 22:55:19 2017 -0700
@@ -44,19 +44,6 @@
         pinned.update(rev(t[0]) for t in tags.values() if t[0] in nodemap)
     return pinned
 
-def _consistencyblocker(pfunc, hideable, revs):
-    """return non-hideable changeset blocking hideable one
-
-    For consistency, we cannot actually hide a changeset if one of it children
-    are visible, this function find such children.
-    """
-    blockers = set()
-    for r in revs:
-        for p in pfunc(r):
-            if p != nullrev and p in hideable:
-                blockers.add(r)
-                break
-    return blockers
 
 def _revealancestors(pfunc, hidden, revs):
     """reveals contiguous chains of hidden ancestors of 'revs' by removing them
@@ -89,16 +76,12 @@
         mutablephases = (phases.draft, phases.secret)
         mutable = repo._phasecache.getrevset(repo, mutablephases)
 
-        visible = mutable - hidden
-        blockers = _consistencyblocker(pfunc, hidden, visible)
-
-        # check if we have wd parents, bookmarks or tags pointing to hidden
-        # changesets and remove those.
-        blockers |= (hidden & pinnedrevs(repo))
-        if blockers:
+        visible = set(mutable - hidden)
+        visible |= (hidden & pinnedrevs(repo))
+        if visible:
             # don't modify possibly cached result of hideablerevs()
             hidden = hidden.copy()
-            _revealancestors(pfunc, hidden, blockers)
+            _revealancestors(pfunc, hidden, visible)
     return frozenset(hidden)
 
 def computeunserved(repo):