Remove useless OpenSSL warning from configure script

There's a OpenSSL warning in configure script that's obsolete:

The latest stable version is the 1.1.0 series. The 1.0.2 series is our Long Term Support (LTS) release, supported until 31st December 2019. The 0.9.8, 1.0.0 and 1.0.1 versions are now out of support and should not be used.

and it should be removed as it is not BIND's place to teach users to update their system anyway.