Don't pass "-b" to gsutil when downloading go tool binaries.

Don't pass "-b" to gsutil when downloading go tool binaries.

Recently updated gsutil in depot_tools doesn't offer the "-b"
(bypass_prodaccess) flag anymore, causing the download to fail:

________ running '/usr/bin/python src/tools/go/download.py' in
'/home/ppi/projects/mojo'
CommandException: option -b not recognized
Running ['python', '/home/ppi/Install/depot_tools/gsutil.py', '-b',
'cp',
'gs://mojo/go/tool/390daacbfac646491c8ac7469195105ac0ce2c46.tar.gz',
'/home/ppi/projects/mojo/src/third_party/go/tool/go.tar.gz']
Failed.
WARNING: Failed to download Go tool binaries.

Skipping "-b" makes the download work a public network, presumably it is
not needed anymore?

R=rogulenko@google.com

Committed: https://chromium.googlesource.com/external/mojo/+/97b3360decaf5d0fa129f67e6648e7b81516d6fb

[ppi, 2015-07-19 16:05:11]

ppi@chromium.org changed reviewers:
+ rogulenko@google.com, viettrungluu@chromium.org

[ppi, 2015-07-19 16:06:18]

Hi Trung or Sergey,

ptal.

[rogulenko, 2015-07-20 09:20:52]

lgtm

[ppi, 2015-07-20 13:23:35]

Committed patchset #1 (id:1) manually as
97b3360decaf5d0fa129f67e6648e7b81516d6fb (presubmit successful).