Yank custom agent code and ca-bundle.crt

Avoids funny memory management behaviour in Node.js when using
a custom HTTPS agent with a certificate bundle.

Node 0.10.x+ will now use peer certificate verification by
default, which is what the custom SSL agent was being used for,
so the agent is no longer necessary.

Node 0.8.x users should consider upgrading or passing a custom
agent with `rejectUnauthorized: true` to `httpOptions`:

    AWS.config.httpOptions = {
      agent: new https.Agent({
        rejectUnauthorized: true
      })
    };