AP_Motors: remove unused stabilizing flag

Also initialise some members to resolve converity warnings

libraries/AP_Motors/AP_Motors_Class.cpp

@@ -33,10 +33,12 @@ AP_Motors::AP_Motors(uint16_t loop_rate, uint16_t speed_hz) :
     _yaw_in(0.0f),
     _throttle_in(0.0f),
     _throttle_filter(),
+    _spool_desired(DESIRED_SHUT_DOWN),
     _batt_voltage(0.0f),
     _batt_current(0.0f),
     _air_density_ratio(1.0f),
-    _motor_map_mask(0)
+    _motor_map_mask(0),
+    _motor_fast_mask(0)
 {
     // init other flags
     _flags.armed = false;

libraries/AP_Motors/AP_Motors_Class.h

@@ -151,7 +151,6 @@ protected:
     // flag bitmask
     struct AP_Motors_flags {
         uint8_t armed              : 1;    // 0 if disarmed, 1 if armed
-        uint8_t stabilizing        : 1;    // 0 if not controlling attitude, 1 if controlling attitude
         uint8_t frame_orientation  : 4;    // PLUS_FRAME 0, X_FRAME 1, V_FRAME 2, H_FRAME 3, NEW_PLUS_FRAME 10, NEW_X_FRAME, NEW_V_FRAME, NEW_H_FRAME
         uint8_t interlock          : 1;    // 1 if the motor interlock is enabled (i.e. motors run), 0 if disabled (motors don't run)
     } _flags;