src: fix build error without OpenSSL support
PR #3890 [1] introduced the variable ALLOW_INSECURE_SERVER_DHPARAM
defined in src/node_crypto.cc. However, if node is built without OpenSSL support, the build fails:
error: ‘ALLOW_INSECURE_SERVER_DHPARAM’ was not declared in this scope
ALLOW_INSECURE_SERVER_DHPARAM = true;
Fix this by using the preprocessor macro HAVE_OPENSSL to opt-out the use of ALLOW_INSECURE_SERVER_DHPARAM
in non-OpenSSL builds.