Due to commit [gnupg: upgrade 2.5.0 -> 2.5.1] applied, drop
gpg2 and use gpg to instead
(From OE-Core rev: ff50a4aba5394dc7c19a862f2cfbcd46ff9d6079)
Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>