Remove useless variables

cost_function.py

@@ -125,9 +125,6 @@ for yr in range(1993, 2019):
         # calculate the indexes and dates
         first = report_graph.node_to_date_eddy(segment[0], e_overestim)
         
-        # get days since 1950
-        first_days = first['date_index']
-        
         # get year
         first_date = datetime.date(1950, 1, 1) \
             + datetime.timedelta(first['date_index'])
@@ -140,12 +137,7 @@ for yr in range(1993, 2019):
             
             # start processing
             
-            first_pos = []
-            last_pos = []
-            
             last = report_graph.node_to_date_eddy(segment[-1], e_overestim)
-            last_days = last['date_index']
-            
             last_date = datetime.date(1950, 1, 1) \
                 + datetime.timedelta(last['date_index'])
             last_year = last_date.year