net/http/cgi: remove outdated TODO
net/http/cgi: remove outdated TODO

Cookies already work as http.Request parses the Cookie header on-demand
when the Cookie methods are called.

Change-Id: Ib7a6f68be02940ff0b56d2465c94545d6fd43847
Reviewed-on: https://go-review.googlesource.com/c/go/+/221417
Reviewed-by: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>
Run-TryBot: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

cloudflare/go,akutz/go,akutz/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,cloudflare/go,golang/go,akutz/go,akutz/go,CAFxX/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,cloudflare/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,akutz/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,akutz/go,golang/go,nawawi/go,golang/go,akutz/go,CAFxX/go,akutz/go,nawawi/go,golang/go,nawawi/go,nawawi/go,golang/go,cloudflare/go