The ad hoc task core_course\task\course_delete_modules can be instantiated with custom data of several modules to delete. Currently if one of these modules cannot be deleted and an error is raised, then it will block the remaining modules.

This patch handles this condition, allowing all modules that can be deleted to be deleted. An error on the task is still thrown if there are modules that cannot be deleted.

Also the task will be updated to use the "no retry" flag, so the task only runs once. This is because if one or modules cannot be deleted there is no point retrying as the condition will persist.