src: guard bundled_ca/openssl_ca with HAVE_OPENSSL

Currently, the following warning will be reported when configuring
without-ssl:

../src/node.cc:3653:8: warning: unused variable 'use_bundled_ca'
[-Wunused-variable]
  bool use_bundled_ca = false;
       ^
../src/node.cc:3654:8: warning: unused variable 'use_openssl_ca'
[-Wunused-variable]
  bool use_openssl_ca = false;
       ^

I missed this when working on
commit 8a7db9d4 ("src: add
--use-bundled-ca --use-openssl-ca check").

Refs: https://github.com/nodejs/node/pull/12087
PR-URL: https://github.com/nodejs/node/pull/12302


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>