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

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

src