src: Fix remaining #include <timer.h>

Follow-up to add76f91d5 (src: Use #include <timer.h> when appropriate).

Change-Id: I7813daa0b73039ec76d33a16ce3ae0ce6cc7f2cc
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32232
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/include/thread.h

@@ -18,7 +18,6 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <bootstate.h>
-#include <timer.h>
 #include <arch/cpu.h>
 
 #if CONFIG(COOP_MULTITASKING) && !defined(__SMM__) && !defined(__PRE_RAM__)