Remove uneeded import from code example

This had me reread the code twice to see if I missed why the import was
present.

diff --git a/lib/sqlalchemy/ext/mutable.py b/lib/sqlalchemy/ext/mutable.py
index 82410031d02efa19b850ed5e94c0489dc72cd990..4e574935d8c33cc36fc52d18bea5557aa960dc34 100644 (file)
--- a/lib/sqlalchemy/ext/mutable.py
+++ b/lib/sqlalchemy/ext/mutable.py
@@ -49,7 +49,6 @@ tracks all parents which reference it.  Below, we illustrate the a simple
 version of the :class:`.MutableDict` dictionary object, which applies
 the :class:`.Mutable` mixin to a plain Python dictionary::
 
-    import collections
     from sqlalchemy.ext.mutable import Mutable
 
     class MutableDict(Mutable, dict):