* src/gpgme-json.c: Remove header argparse.h. Define
GPGRT_ENABLE_ARGPARSE_MACROS.
(interactive_repl): Replace strusage by gpgrt_strusage.
(my_strusage): Add SPDX level.
(main): Switch to gpgrt_argparse stuff but keep very limited
functionality when building with an older libgpg-error.
Signed-off-by: Werner Koch <wk@gnupg.org>