[release-branch.go1.4] [release-branch.go1.4] doc: scrub references to code.google.com

These are the references that affect current Go users.
I left intact references in older release notes;
we can figure out what to do with them later.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://codereview.appspot.com/186140043
[release-branch.go1.4] api: create go1.4.txt

I read through and vetted these but others should look too.

LGTM=bradfitz, adg
R=r, minux, bradfitz, adg
CC=adg, golang-codereviews, gri, iant
https://codereview.appspot.com/182560043

Committer: Andrew Gerrand <adg@golang.org>