kbuild: Drop support for include/asm-<arch> in headers_check.pl

"include/asm-<arch>" was replaced by "arch/<arch>/include/asm" a long
time ago.  All assembler header files are now included using
"#include <asm/*>", so there is no longer a need to rewrite paths.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>