Require the latest GpgRT and drop old substitutions.
* configure.ac: Require GpgRT 1.56 * common/util.h: Remove errot code substitutions. * common/argparse.h: Remove almost all code. Just keep the wrappers for GpgRT. * common/argparse.c: Ditto.. * common/sysutils.c (gnupg_getcwd): Ditto. (gnupg_access): Ditto. * sm/gpgsm.c (main): Remove condition for old GpgRTs. * tools/gpgconf.c (my_read_reg_string): Ditto.
One of the latest bug fixes was only tested with the latest GpgRT and
thus it does not make sense to keep support for older versions.