kbuild: deb-pkg: do not run headers_check

It is absolutely fine to add extra sanity checks in package scripts,
but it is not necessary to do so.

This is already covered by the daily compile-testing (0day bot etc.)
because headers_check is run as a part of the normal build process
when CONFIG_HEADERS_CHECK=y.

Replace it with the newly-added "make headers".

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>