revlog: remove delta function

mercurial/manifest.py

@@ -35,7 +35,8 b' class manifest(revlog):'
         return mfdict
 
     def readdelta(self, node):
-        return self.parse(mdiff.patchtext(self.delta(node)))
+        r = self.rev(node)
+        return self.parse(mdiff.patchtext(self.revdiff(r - 1, r)))
 
     def read(self, node):
         if node == nullid: return manifestdict() # don't upset local cache

mercurial/revlog.py

@@ -941,11 +941,6 b' class revlog(object):'
 
         return decompress(c)
 
-    def delta(self, node):
-        """return or calculate a delta between a node and its predecessor"""
-        r = self.rev(node)
-        return self.revdiff(r - 1, r)
-
     def revdiff(self, rev1, rev2):
         """return or calculate a delta between two revisions"""
         if rev1 + 1 == rev2 and self.base(rev1) == self.base(rev2):