crypto: unbreak build with no-NPN shared openssl

Unbreak the build when linking against a shared version of OpenSSL that
doesn't support NPN (Next Protocol Negotiation.)

Fixes the following build error:

  ../src/node_crypto.cc:140: error: no member function
  'AdvertiseNextProtoCallback' declared in
  'node::crypto::SSLWrap<node::TLSCallbacks>'
  ../src/node_crypto.cc:147: error: no member function
  'SelectNextProtoCallback' declared in
  'node::crypto::SSLWrap<node::TLSCallbacks>'