Drop G+ links from the site docs

Change-Id: I0eab90e068cb3caf31f0e87f134a79e2573c8aab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1738009Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700982}

chrome/common/extensions/docs/templates/private/site.html

@@ -69,8 +69,6 @@
         </div>
         <div class="g-unit g-last">
           <div id="social-buttons">
-            <div data-size="small" data-href="http://www.google.com/chrome" data-annotation="bubble" class="g-plusone"></div>
-            <a rel="publisher" target="_blank" href="https://plus.google.com/+GoogleChromeDevelopers?prsrc=3" data-g-label="plus" data-g-event="nav-subfooter">Add us on <span class="element-invisible">Google+</span><img src="//ssl.gstatic.com/images/icons/gplus-16.png" data-g-label="plus" data-g-event="nav-subfooter" alt=""></a>
           </div>
         </div>
       </div>