Tools/calibration: Optimized the memory usage in loops.

Dict.items() generate intermediate result lists several times, fixed for loops
to use dict automatic iteration instead.
And use dict in place update instead of build new intermediate dict if possible.

modules/tools/calibration/result2pb.py

@@ -42,21 +42,25 @@ def load_calibration_raw_data(fn):
                 cmd_table = {}
                 cmd_table[cmd] = [acc]
                 speed_table[speed] = cmd_table
-    for speed, cmd_table in speed_table.items():
-        new_cmd_table = {}
-        for cmd, acc_list in cmd_table.items():
-            new_cmd_table[cmd] = round(np.mean(acc_list), 2)
-        speed_table[speed] = new_cmd_table
+                
+    for speed in speed_table:
+        cmd_table = speed_table[speed]
+        for cmd in cmd_table:
+            cmd_table[cmd] = round(np.mean(cmd_table[cmd]), 2)
+    #After this the acc_list converted to an average float number.
 
     speed_table2 = {}
-    for speed, cmd_table in speed_table.items():
+    for speed in speed_table:
+        cmd_table = speed_table[speed]
         acc_table = {}
-        for cmd, acc in cmd_table.items():
+        for cmd in cmd_table: 
+            acc = cmd_table[cmd]
             if acc in acc_table:
                 acc_table[acc].append(cmd)
             else:
                 acc_table[acc] = [cmd]
         speed_table2[speed] = acc_table
+
     return speed_table2
 
 def load_calibration_raw_data_old(fn):