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/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,