Remove unused --with-openssl configure option, Issue #4456.

This hasn't had a use since 1.7.0 when we removed the ability to build
neon in-tree.

* configure.ac
  (): Remove definition of --with-openssl.



git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1548714 13f79535-47bb-0310-9956-ffa450edef68