Bug 851646: remove unused strings, r=mixedpuppy

browser/locales/en-US/chrome/browser/browser.properties

@@ -390,8 +390,6 @@ social.turnOn.accesskey=T
 social.error.message=%1$S is unable to connect with %2$S right now.
 social.error.tryAgain.label=Try Again
 social.error.tryAgain.accesskey=T
-social.error.ok.label=OK
-social.error.ok.accesskey=O
 social.error.closeSidebar.label=Close This Sidebar
 social.error.closeSidebar.accesskey=C