Revert "Feature/len (#68)"

This reverts commit 705d024993.

gym/spaces/discrete.py

@@ -21,5 +21,3 @@ class Discrete(Space):
         return "Discrete(%d)" % self.n
     def __eq__(self, other):
         return self.n == other.n
-    def __len__(self):
-        return  n

gym/spaces/tuple_space.py

@@ -7,9 +7,6 @@ class Tuple(Space):
     def __init__(self, spaces):
         self.spaces = spaces
 
-    def __len__(self):
-        return len(self.spaces)
-
     def sample(self):
         return tuple([space.sample() for space in self.spaces])