Do not support CentOS 6 anymore
Since the EOL has reached to RHEL6 / CentOS6 I do not intend to support that system anymore. This means we can remove some ifdefs from the openssl backend.
Since the EOL has reached to RHEL6 / CentOS6 I do not intend to support that system anymore. This means we can remove some ifdefs from the openssl backend.