tests,json: Move version check into t-json
* tests/gpg/t-support.h (check_gpg_version, compare_versions), (parse_version_string, parse_version_number): Remove version check code. * tests/json/t-json.c (check_gpg_version, compare_versions), (parse_version_string, parse_version_number): Add.
t-support header was not a good place for this. It should
go into a library e.g. gpgrt in the future. For now we
can keep it close to where it is needed.