Also switches the download url to the non-deprecated gs direct download URL, and
remove an ancient README.google that talked about software that's no longer
distributed.

R=dnj@chromium.org, agable@chromium.org, maruel@chromium.org, mmoss@chromium.org
BUG=598958

Review URL: https://codereview.chromium.org/1851433005 .

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299622 0039d316-1c4b-4281-b951-d872f2087c98