util: simplify range expression

The n index variable was unused. Every iteration would pop one element
off of parts, so the for loop can be replaced with a while loop.

mercurial/util.py

@@ -512,7 +512,7 b' class path_auditor(object):'
                                 (path, prefix))
         parts.pop()
         prefixes = []
-        for n in range(len(parts)):
+        while parts:
             prefix = os.sep.join(parts)
             if prefix in self.auditeddir:
                 break