removes unused setter, moves inputs construction for WeightedCost for…

… performance

pybop/costs/_weighted_cost.py

@@ -101,10 +101,10 @@ def compute(
         de = np.empty((len(self.parameters), len(self.costs)))
 
         for i, cost in enumerate(self.costs):
-            inputs = cost.parameters.as_dict()
             if self._has_identical_problems:
                 y, dy = (y, dy)
             elif cost.has_separable_problem:
+                inputs = cost.parameters.as_dict()
                 if calculate_grad:
                     y, dy = cost.problem.evaluateS1(inputs)
                 else:

pybop/costs/base_cost.py

@@ -191,10 +191,6 @@ def n_parameters(self):
     def has_separable_problem(self):
         return self._has_separable_problem
 
-    @has_separable_problem.setter
-    def has_separable_problem(self, has_separable_problem):
-        self._has_separable_problem = has_separable_problem
-
     @property
     def target(self):
         return self._target