Checking bucket permissions takes ~400ms. We don't
need to do this if --no-auth because we know we
won't get a 403 and the 404 check will be handled
later when we try to actually download the file.

Also, remove the check for a null bucket. This
can't happen since we will throw a parser error
in the main function before we get to this code.

R=iannucci@chromium.org

Review URL: https://codereview.chromium.org/772203002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@293250 0039d316-1c4b-4281-b951-d872f2087c98