Refactor prior to adding task-page

appengine/swarming/elements/res/imp/botpage/bot-page-shared-behavior.html

 <!--
   Copyright 2016 The LUCI Authors. All rights reserved.
   Use of this source code is governed under the Apache License, Version 2.0
   that can be found in the LICENSE file.
 
   window.SwarmingBehaviors.BotPageBehavior contains any shared functions and
   constants used by the bot-page and its sub-elements.
 
   To use it, include
       behaviors: [SwarmingBehaviors.BotPageBehavior]
   in the creation of your Polymer element.
 -->
 <link rel="import" href="/res/imp/common/common-behavior.html">
 <script>
   (function(){
 
 
     // This behavior wraps up all the shared bot-page functionality by
     // extending SwarmingBehaviors.CommonBehavior
     SwarmingBehaviors.BotPageBehavior = [SwarmingBehaviors.CommonBehavior, {
 
-      // timeDiffApprox returns the approximate difference between now and
-      // the specified date.
-      _timeDiffApprox: function(date){
-        if (!date) {
-          return "eons";
-        }
-        return sk.human.diffDate(date.getTime());
-      },
-
-      // timeDiffExact returns the exact difference between the two specified
-      // dates.  E.g. 2d 22h 22m 28s ago If a second date is not provided,
-      // now is used.
-      _timeDiffExact: function(first, second){
-        if (!first) {
-          return "eons";
-        }
-        if (!second) {
-          second = new Date();
-        }
-        return sk.human.strDuration((second.getTime() - first.getTime())/1000);
-      },
-
     }];
   })()
 </script>