mail.google.com.js

// ==UserScript==
// @author     Jagadeesh
// @name           Remove Contextual Gadgets from Gmail
// @namespace
// @description    Removes Contextual Gadgets/widgets from footer of email messages in Gmail.
// @include        https://mail.google.*
// @include        http://mail.google.*
// ==/UserScript==

(function(){
  var css="\
  div.gs div.hi {\
    display: none !important;\
  }\
  ";

  if (typeof GM_addStyle != "undefined") {
    GM_addStyle(css);
  } else if (typeof PRO_addStyle != "undefined") {
    PRO_addStyle(css);
  } else if (typeof addStyle != "undefined") {
    addStyle(css);
  } else {
    var heads = document.getElementsByTagName("head");
    if (heads.length > 0) {
      var node = document.createElement("style");
      node.type = "text/css";
      node.appendChild(document.createTextNode(css));
      heads[0].appendChild(node);
    }
  }
})();