libpayload: Remove legacy CBFS API

It's been several years already since we announced the deprecation of
the legacy CBFS API for payloads. It's time to remove it completely.

Change-Id: I0ed157ac2d1376b8dff4537af9a63731064b45f6
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80650
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Jakub Czapiga <czapiga@google.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Maximilian Brune <maximilian.brune@9elements.com>

payloads/libpayload/arch/mock/Makefile.mk

@@ -4,6 +4,4 @@ head.o-y += head.c
 
 libc-y += virtual.c
 
-libcbfs-$(CONFIG_LP_CBFS) += mock_media.c
-
 CFLAGS += -Wno-address-of-packed-member