manifest: remove unused property _oldmanifest
The last use seems to have gone away in
7c7d845f8b64 (manifest: make
manifestlog use it's own cache, 2016-11-10).
--- a/mercurial/manifest.py Fri May 05 04:48:42 2017 +0530
+++ b/mercurial/manifest.py Mon May 08 09:39:21 2017 -0700
@@ -1317,8 +1317,7 @@
cachesize = opts.get('manifestcachesize', cachesize)
self._treeinmem = usetreemanifest
- self._oldmanifest = repo._constructmanifest()
- self._revlog = self._oldmanifest
+ self._revlog = repo._constructmanifest()
# A cache of the manifestctx or treemanifestctx for each directory
self._dirmancache = {}