Remove prio_list.

	Remove prio_list.

	* include/grub/list.h (grub_prio_list): Removed.
	(GRUB_PRIO_LIST_PRIO_MASK): Removed. All users switched to
	GRUB_COMMAND_PRIO_MASK.
	(GRUB_PRIO_LIST_FLAG_ACTIVE): Removed. All users switched to
	GRUB_COMMAND_FLAG_ACTIVE.
	(grub_prio_list_insert): Removed.
	(grub_prio_list_remove): Likewise.
	(GRUB_AS_PRIO_LIST): Likewise.
	(GRUB_AS_PRIO_LIST_P): Likewise.
	* include/grub/command.h (GRUB_COMMAND_PRIO_MASK): New define.
	(GRUB_COMMAND_FLAG_ACTIVE): Likewise.
	* grub-core/kern/list.c (grub_prio_list_insert): Remove.
	* grub-core/kern/command.c (grub_register_command_prio): Inline
	the prio_list code.
	(grub_unregister_command): Likewise.