Removed useless statement:

It was added by James in f062502a097c but he does not remember why it was there. It looks like it was never used.

Removed useless statement:
ff8d1e25 · Olivier Delalleau · a8b47a81 · ff8d1e25
--- a/theano/configparser.py
+++ b/theano/configparser.py
@@ -235,9 +235,6 @@ class ConfigParam(object):
        else:
            self.val = val

-    # TODO What is this for?
-    deleter = None
-

 class EnumStr(ConfigParam):
    def __init__(self, default, *options, **kwargs):