Remove thread callbacks for libgcrypt >= 1.6.
* agent/gpg-agent.c (GCRY_THREAD_OPTION_PTH_IMPL): Do not use with libgcrypt >= 1.6. (main): Ditto. * scd/scdaemon.c (GCRY_THREAD_OPTION_PTH_IMPL): Ditto. (main): Ditto.
This is not anymore needed but kept for compatibility with Libgcrypt <
1.6.