#759 remove unneeded _variables from base_model

Author: martinjrobins

pybamm/models/base_model.py

@@ -105,7 +105,6 @@ def __init__(self, name="Unnamed model"):
         self._algebraic = {}
         self._initial_conditions = {}
         self._boundary_conditions = {}
-        self._variables = {}
         self._variables = pybamm.FuzzyDict()
         self._events = []
         self._concatenated_rhs = None