Don't import jQuery on Anki 2.1

2.1 already ships with its own jQuery build, so there's no need
to import our own.

Fixes an issue where the add-on would only work after restarting
Anki 2.1 at least once. Perhaps because of caching jQuery?

src/popup_dictionary/web.py

@@ -318,5 +318,5 @@
 <script>{}</script>
 <script>{}</script>
 <script>{}</script>
-""".format(qtip_css, tooltip_css, jquery_js,
+""".format(qtip_css, tooltip_css, jquery_js if not anki21 else "",
            qtip_js, highlight_js, tooltip_script_js)