match: remove unnecessary setting of self._always

The 'always' class calls its parent constructor with an empty list of
patterns, which will result in a matcher that always matches. The
parent constructor will set self._always to True in such cases, so
there is no need to set it again.

mercurial/match.py

@@ -156,7 +156,6 b' class exact(match):'
 class always(match):
     def __init__(self, root, cwd):
         match.__init__(self, root, cwd, [])
-        self._always = True
 
 class narrowmatcher(match):
     """Adapt a matcher to work on a subdirectory only.