customizer: minor cleanup of IE8 error messaging code

[skip sauce]

docs/customize.html

@@ -7,7 +7,6 @@ lead: Customize Bootstrap's components, Less variables, and jQuery plugins to ge
 
 <!-- less.js isn't IE8-compatible and throws an exception during initialization, so our Blob compatibility check and error messaging code never get called in that case.
   So we use a conditional comment instead to inform folks about the lack of IE8 support.
-  The alert covers up the entire customizer UI.
 -->
 <!--[if lt IE 9]>
   <style>
@@ -17,7 +16,7 @@ lead: Customize Bootstrap's components, Less variables, and jQuery plugins to ge
       display: none;
     }
   </style>
-  <div class="alert alert-danger bs-customizer-alert-ie">
+  <div class="alert alert-danger">
     <strong>The Bootstrap Customizer does not support IE9 and below.</strong><br>
     Please take a second to <a href="http://browsehappy.com/">upgrade to a more modern browser</a>.
   </div>