Fixes for posix-arm and qurt builds

Ifdefed out deadcode in position_estimator_inav_main.c as the
deadcode does not compile for qurt.

Added fixes to get a successful build for posix-arm and qurt targets.
Removed CLOCK_REALTIME def from px4_time.h for qurt and removed unused
variables in att_est_q and mc_att_control.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/modules/mc_att_control/mc_att_control_main.cpp

@@ -137,7 +137,6 @@ private:
 	int		_vehicle_status_sub;	/**< vehicle status subscription */
 	int 	_motor_limits_sub;		/**< motor limits subscription */
 
-	orb_advert_t	_att_sp_pub;			/**< attitude setpoint publication */
 	orb_advert_t	_v_rates_sp_pub;		/**< rate setpoint publication */
 	orb_advert_t	_actuators_0_pub;		/**< attitude actuator controls publication */
 	orb_advert_t	_controller_status_pub;	/**< controller status publication */
@@ -170,8 +169,6 @@ private:
 
 	math::Matrix<3, 3>  _I;				/**< identity matrix */
 
-	bool	_reset_yaw_sp;			/**< reset yaw setpoint flag */
-
 	struct {
 		param_t roll_p;
 		param_t roll_rate_p;
@@ -315,7 +312,6 @@ MulticopterAttitudeControl::MulticopterAttitudeControl() :
 	_vehicle_status_sub(-1),
 
 /* publications */
-	_att_sp_pub(nullptr),
 	_v_rates_sp_pub(nullptr),
 	_actuators_0_pub(nullptr),
 	_controller_status_pub(nullptr),