It is not used outside of builtin-check.c.

Also remove the unused declaration from builtin.h .
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20221216-objtool-memory-v2-2-17968f85a464@weissschuh.netSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>