ASSERT: remove some inappropriate asserts

Since assertions lead to crashes, we need better failure handling. In all
the cases in this patch, the assert is not required.

All the ones with the task id should be replaced with the module base
class.

Ah yes, and this reduces flash space, since the ASSERT macro will expand to
a printf that contains the source file name.

src/drivers/px4io/px4io.cpp

@@ -590,8 +590,6 @@ PX4IO::init()
 	param_t sys_restart_param;
 	int32_t sys_restart_val = DM_INIT_REASON_VOLATILE;
 
-	ASSERT(_task == -1);
-
 	sys_restart_param = param_find("SYS_RESTART_TYPE");
 
 	if (sys_restart_param != PARAM_INVALID) {

src/modules/camera_feedback/camera_feedback.cpp

@@ -93,8 +93,6 @@ int
 CameraFeedback::start()
 {
 
-	ASSERT(_main_task == -1);
-
 	/* start the task */
 	_main_task = px4_task_spawn_cmd("camera_feedback",
 					SCHED_DEFAULT,

src/modules/events/temperature_calibration/task.cpp

@@ -328,7 +328,6 @@ void TemperatureCalibration::do_temperature_calibration(int argc, char *argv[])
 int TemperatureCalibration::start()
 {
 
-	ASSERT(_control_task == -1);
 	_control_task = px4_task_spawn_cmd("temperature_calib",
 					   SCHED_DEFAULT,
 					   SCHED_PRIORITY_MAX - 5,

src/modules/mc_pos_control/mc_pos_control_main.cpp

@@ -3368,8 +3368,6 @@ MulticopterPositionControl::landdetection_thrust_limit(matrix::Vector3f &thrust_
 int
 MulticopterPositionControl::start()
 {
-	ASSERT(_control_task == -1);
-
 	/* start the task */
 	_control_task = px4_task_spawn_cmd("mc_pos_control",
 					   SCHED_DEFAULT,

src/modules/uORB/uORBManager.cpp

@@ -319,7 +319,6 @@ int uORB::Manager::orb_set_interval(int handle, unsigned interval)
 
 int uORB::Manager::orb_get_interval(int handle, unsigned *interval)
 {
-	ASSERT(interval);
 	int ret = px4_ioctl(handle, ORBIOCGETINTERVAL, (unsigned long)interval);
 	*interval /= 1000;
 	return ret;

src/modules/vtol_att_control/vtol_att_control_main.cpp

@@ -767,8 +767,6 @@ void VtolAttitudeControl::task_main()
 int
 VtolAttitudeControl::start()
 {
-	ASSERT(_control_task == -1);
-
 	/* start the task */
 	_control_task = px4_task_spawn_cmd("vtol_att_control",
 					   SCHED_DEFAULT,