security/rubygem-gpgme: Adapt for GpgME 2.0.0
The trustlist feature, which only worked for a short period in 2003, was
removed in GpgME 2.0.0.
The gpgme_attr_t enums and their functions, which have been marked deprecated
since 2003, were removed in GpgME 2.0.0.