src: Remove unused <cbmem.h>

Change-Id: I2279e2d7e6255a88953b2485c1f1a3b51a72c65e
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50182
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/lib/metadata_hash.c

@@ -2,7 +2,6 @@
 /* This file is part of the coreboot project. */
 
 #include <assert.h>
-#include <cbmem.h>
 #include <metadata_hash.h>
 #include <symbols.h>