Remove a Blink left-over of "gcm_user_visible_only".

Remove a Blink left-over of "gcm_user_visible_only".

Support has been removed per the following CL. All consumers will now have
to use the PushSubscriptionOptions dictionary.

https://codereview.chromium.org/1158923002/

BUG=471534
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196337

[Peter Beverloo, 2015-05-27 13:03:14]

peter@chromium.org changed reviewers:
+ johnme@chromium.org

[johnme, 2015-05-28 11:01:25]

lgtm

[Peter Beverloo, 2015-06-02 15:59:08]

The CQ bit was checked by peter@chromium.org

[commit-bot: I haz the power, 2015-06-02 15:59:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1156283002/1

[commit-bot: I haz the power, 2015-06-02 17:11:53]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-02 17:11:54]

Try jobs failed on following builders:
  linux_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/6...)

[Peter Beverloo, 2015-06-02 17:14:23]

The CQ bit was checked by peter@chromium.org

[commit-bot: I haz the power, 2015-06-02 17:15:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1156283002/1

[commit-bot: I haz the power, 2015-06-02 19:06:50]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196337