http: Remove an unnecessary assignment

This just removes an assignment to `ret` of a value that's not used before
it's overwritten.  Immediately following the assigment is an `if/else` in
which both branches assign to `ret` without using it.

PR-URL: https://github.com/nodejs/node/pull/4323


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: James M Snell <jasnell@gmail.com>