Replace MSG_F? with MSG_N?

To avoid double definitions.
I prefer to read N for Number not for Nozzle.

Marlin/language_cn.h

   #define MSG_MOVE_10MM                       "\xc1\xb2 10mm"
   #define MSG_SPEED                           "\xd1\xd2"
   #define MSG_NOZZLE                          "\xd3\xd4"
+  #define MSG_N0                              " 0"
+  #define MSG_N1                              " 1"
   #define MSG_N2                              " 2"
   #define MSG_N3                              " 3"
   #define MSG_N4                              " 4"
   #define MSG_BED                             "\xc4\xc7"
   #define MSG_FAN_SPEED                       "\xd5\xd6\xd1\xd2"
   #define MSG_FLOW                            "\xcc\xad\xd1\xd2"
-  #define MSG_F0                              " 0"
-  #define MSG_F1                              " 1"
-  #define MSG_F2                              " 2"
-  #define MSG_F3                              " 3"
   #define MSG_CONTROL                         "\xd8\xd9"
   #define MSG_MIN                             LCD_STR_THERMOMETER " \xda\xdb"
   #define MSG_MAX                             LCD_STR_THERMOMETER " \xda\xdc"

Marlin/language_en.h

 #ifndef MSG_NOZZLE
 #define MSG_NOZZLE                          "Nozzle"
 #endif
+#ifndef MSG_N0
+#define MSG_N0                              " 0"
+#endif
+#ifndef MSG_N1
+#define MSG_N1                              " 1"
+#endif
 #ifndef MSG_N2
 #define MSG_N2                              " 2"
 #endif
 #ifndef MSG_FLOW
 #define MSG_FLOW                            "Flow"
 #endif
-#ifndef MSG_F0
-#define MSG_F0                              " 0"
-#endif
-#ifndef MSG_F1
-#define MSG_F1                              " 1"
-#endif
-#ifndef MSG_F2
-#define MSG_F2                              " 2"
-#endif
-#ifndef MSG_F3
-#define MSG_F3                              " 3"
-#endif
 #ifndef MSG_CONTROL
 #define MSG_CONTROL                         "Control"
 #endif

Marlin/ultralcd.cpp

   #endif
   MENU_MULTIPLIER_ITEM_EDIT(int3, MSG_FAN_SPEED, &fanSpeed, 0, 255);
   MENU_ITEM_EDIT(int3, MSG_FLOW, &extruder_multiply[active_extruder], 10, 999);
-  MENU_ITEM_EDIT(int3, MSG_FLOW MSG_F0, &extruder_multiply[0], 10, 999);
+  MENU_ITEM_EDIT(int3, MSG_FLOW MSG_N0, &extruder_multiply[0], 10, 999);
   #if TEMP_SENSOR_1 != 0
-    MENU_ITEM_EDIT(int3, MSG_FLOW MSG_F1, &extruder_multiply[1], 10, 999);
+    MENU_ITEM_EDIT(int3, MSG_FLOW MSG_N1, &extruder_multiply[1], 10, 999);
   #endif
   #if TEMP_SENSOR_2 != 0
-    MENU_ITEM_EDIT(int3, MSG_FLOW MSG_F2, &extruder_multiply[2], 10, 999);
+    MENU_ITEM_EDIT(int3, MSG_FLOW MSG_N2, &extruder_multiply[2], 10, 999);
   #endif
   #if TEMP_SENSOR_3 != 0
-    MENU_ITEM_EDIT(int3, MSG_FLOW MSG_F3, &extruder_multiply[3], 10, 999);
+    MENU_ITEM_EDIT(int3, MSG_FLOW MSG_N3, &extruder_multiply[3], 10, 999);
   #endif
 
   #ifdef BABYSTEPPING