net/http: fix for recent go.mod update

net/http: fix for recent go.mod update

cmd/internal/moddeps was failing.
Ran the commands it suggested:

% go mod tidy                               # to remove extraneous dependencies
% go mod vendor                             # to vendor dependencies
% go generate -run=bundle std               # to regenerate bundled packages
% go generate syscall internal/syscall/...  # to regenerate syscall packages

cmd/internal/moddeps is happy now.

Change-Id: I4ee212cdc323f62a6cdcfdddb6813397b23d89e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/403454
Run-TryBot: Russ Cox <rsc@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>