Revert "Using lru_cache when available for definitions"

This reverts commit 4b2ebcb.

Author: metatoaster

src/calmjs/parse/unparsers/walker.py

@@ -6,14 +6,6 @@
 
 from __future__ import unicode_literals
 
-try:
-    from functools import lru_cache
-except ImportError:  # pragma: no cover
-    def lru_cache(*a, **kw):
-        def wrapper(f):
-            return f
-        return wrapper
-
 from calmjs.parse.asttypes import Node
 from calmjs.parse.ruletypes import Token
 from calmjs.parse.ruletypes import Structure
@@ -162,7 +154,6 @@ def __init__(
 
         self.__optimized_definitions = self.optimize()
 
-    @lru_cache(maxsize=None)
     def optimize_definition(self, name, definition):
         rules = []
         for rule in definition: