changelog: remove copy of revlog.nodemap()

changelog: remove copy of revlog.nodemap()

It's been there since 2012, "clfilter: introduce `filteredrevs` attribute
on changelog." I don't think we can apply changelog filtering to nodemap at
this level, so this patch removes the nodemap stub completely.

--- a/mercurial/changelog.py	Fri Aug 17 10:51:05 2018 +0900
+++ b/mercurial/changelog.py	Fri Aug 17 12:48:44 2018 +0900
@@ -22,7 +22,6 @@
     error,
     pycompat,
     revlog,
-    util,
 )
 from .utils import (
     dateutil,
@@ -344,12 +343,6 @@
             if i not in self.filteredrevs:
                 yield i
 
-    @util.propertycache
-    def nodemap(self):
-        # XXX need filtering too
-        self.rev(self.node(0))
-        return self._nodecache
-
     def reachableroots(self, minroot, heads, roots, includepath=False):
         return self.index.reachableroots2(minroot, heads, roots, includepath)