revert: fix($sce): allow IE7 standards mode to pass non-quirks mode test

This reverts commit 637c9b1611c5a75a42048ee1c591521c7031751a.
(ref #3633 and #3646)

The minimum bar for $sce is IE8 in standards mode.  IE7 standards mode
is not supported.  If you must support IE7, you should disable $sce
completely.

  angular.module('ie7support', []).config(function($sceProvider) {
    // Completely disable SCE to support IE7.
    $sceProvider.enabled(false);
  });