http: avoid retaining unneeded memory

Prevent the events listeners of the sockets obtained with the HTTP
upgrade mechanism from retaining unneeded memory.

Ref: https://github.com/nodejs/node/issues/11868
PR-URL: https://github.com/nodejs/node/pull/11926


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>