removed legacy code regarding using_list

Mostly I made the code more consist with the other methods in this file, and also made `using_list` to be more literal (i.e. not to include tuples as well)

removed legacy code regarding using_list
e3c2a9d4 · Razvan Pascanu · f7ec76b7 · e3c2a9d4
--- a/theano/tensor/tensor_grad.py
+++ b/theano/tensor/tensor_grad.py
@@ -734,11 +734,12 @@ def jacobian(expression, wrt, consider_constant=None, warn_type=False,
    assert expression.ndim == 1, \
            "tensor.jacobian expects a 1 dimensional variable as `expression`"

+    using_list = isinstance(wrt, list)
+    using_tuple = isinstance(wrt, tuple)
+
    if isinstance(wrt, (list, tuple)):
-        use_list = True
        wrt = list(wrt)
    else:
-        use_list = False
        wrt = [wrt]

    def inner_function(*args):
@@ -799,10 +800,8 @@ def hessian(cost, wrt, consider_constant=None, warn_type=False,
    using_tuple = isinstance(wrt, tuple)

    if isinstance(wrt, (list, tuple)):
-        use_list = True
        wrt = list(wrt)
    else:
-        use_list = False
        wrt = [wrt]

    hessians = []