revset: drop spanset._contained

revset: drop spanset._contained

All its users inlined it for performance reasons.
(See 1d7a2771aa36 and e2031c8ca4f8)

--- a/mercurial/revset.py	Mon May 05 22:47:14 2014 -0700
+++ b/mercurial/revset.py	Fri Apr 25 23:38:24 2014 -0700
@@ -2764,10 +2764,6 @@
         if self._start < self._end:
             self.reverse()
 
-    def _contained(self, rev):
-        return (rev <= self._start and rev > self._end) or (rev >= self._start
-                and rev < self._end)
-
     def __iter__(self):
         if self._start <= self._end:
             iterrange = xrange(self._start, self._end)