Copter: remove compassmot's compass init and accumulate

when compass mot is started, the main loop has been running so the compass will already have been initialised and have good readings
Also remove unnecessary call to get_primary compass

ArduCopter/compassmot.cpp

@@ -82,9 +82,6 @@ MAV_RESULT Copter::mavlink_compassmot(mavlink_channel_t chan)
     // disable cpu failsafe
     failsafe_disable();
 
-    // initialise compass
-    init_compass();
-
     // default compensation type to use current if possible
     if (battery.has_current()) {
         comp_type = AP_COMPASS_MOT_COMP_CURRENT;
@@ -118,10 +115,6 @@ MAV_RESULT Copter::mavlink_compassmot(mavlink_channel_t chan)
     }
 
     // get initial compass readings
-    last_run_time = millis();
-    while ( millis() - last_run_time < 500 ) {
-        compass.accumulate();
-    }
     compass.read();
 
     // store initial x,y,z compass values
@@ -141,7 +134,7 @@ MAV_RESULT Copter::mavlink_compassmot(mavlink_channel_t chan)
     last_send_time = millis();
 
     // main run while there is no user input and the compass is healthy
-    while (command_ack_start == command_ack_counter && compass.healthy(compass.get_primary()) && motors->armed()) {
+    while (command_ack_start == command_ack_counter && compass.healthy() && motors->armed()) {
         // 50hz loop
         if (millis() - last_run_time < 20) {
             // grab some compass values