scripts/kallsyms: remove last remnants of --page-offset option

The implementation of the --page-offset kallsyms command line option has
been removed, so remove it from the usage string as well.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Michal Marek <mmarek@suse.com>

scripts/kallsyms.c

@@ -76,7 +76,6 @@ static void usage(void)
 {
 	fprintf(stderr, "Usage: kallsyms [--all-symbols] "
 			"[--symbol-prefix=<prefix char>] "
-			"[--page-offset=<CONFIG_PAGE_OFFSET>] "
 			"[--base-relative] < in.map > out.S\n");
 	exit(1);
 }