grep: remove useless while condition

A revised version of 35ba170c0f82 was sent to the list that fixed this
<http://markmail.org/message/jmfuiise5igcyh2m&gt;, but the older version of
the patch was applied.

mercurial/commands.py

@@ -2935,7 +2935,7 b' def grep(ui, repo, pattern, *pats, **opt'
     def matchlines(body):
         begin = 0
         linenum = 0
-        while True and begin < len(body):
+        while begin < len(body):
             match = regexp.search(body, begin)
             if not match:
                 break