ACMotors: remove unused get_num_motors function

Saves about 4 bytes of RAM

libraries/AP_Motors/AP_MotorsHeli.h

@@ -108,11 +108,6 @@ public:
     // enable - starts allowing signals to be sent to motors
     void enable();
 
-    // get basic information about the platform
-    uint8_t get_num_motors() {
-        return 5;
-    };
-
     // motor test
     void output_test();
 

libraries/AP_Motors/AP_MotorsMatrix.h

@@ -34,18 +34,13 @@ public:
 
     // set update rate to motors - a value in hertz
     // you must have setup_motors before calling this
-    virtual void            set_update_rate( uint16_t speed_hz );
+    virtual void        set_update_rate( uint16_t speed_hz );
 
     // set frame orientation (normally + or X)
-    virtual void            set_frame_orientation( uint8_t new_orientation );
+    virtual void        set_frame_orientation( uint8_t new_orientation );
 
     // enable - starts allowing signals to be sent to motors
-    virtual void            enable();
-
-    // get basic information about the platform
-    virtual uint8_t         get_num_motors() {
-        return _num_motors;
-    };
+    virtual void        enable();
 
     // motor test
     virtual void        output_test();

libraries/AP_Motors/AP_MotorsTri.h

@@ -25,18 +25,13 @@ public:
     };
 
     // init
-    virtual void            Init();
+    virtual void        Init();
 
     // set update rate to motors - a value in hertz
-    void                    set_update_rate( uint16_t speed_hz );
+    void                set_update_rate( uint16_t speed_hz );
 
     // enable - starts allowing signals to be sent to motors
-    virtual void            enable();
-
-    // get basic information about the platform
-    virtual uint8_t         get_num_motors() {
-        return 4;
-    };                                                  // 3 motors + 1 tail servo
+    virtual void        enable();
 
     // motor test
     virtual void        output_test();

libraries/AP_Motors/AP_Motors_Class.h

@@ -117,11 +117,6 @@ public:
         return _reached_limit & which_limit;
     }
 
-    // get basic information about the platform
-    virtual uint8_t        get_num_motors() {
-        return 0;
-    };
-
     // motor test
     virtual void        output_test() {
     };