PYTHON-710, simplify SON's equality operator.

Author: ajdavis

bson/son.py

@@ -208,7 +208,7 @@ def __eq__(self, other):
         """
         if isinstance(other, SON):
             return len(self) == len(other) and self.items() == other.items()
-        return self.to_dict() == other
+        return dict.__eq__(self, other)
 
     def __ne__(self, other):
         return not self == other