Removing duplicate custom-jekyll js

After docsy theme got merged these scripts aren't needed anymore.  Confirmed
after removing it (and all `<script>` references to it) the tooltip
functionality is still there.
Also removed the reference in `config.toml` to it, which may have stripped some
dangling whitespace.

static/js/custom-jekyll/tags.js

@@ -1,15 +0,0 @@
-$( document ).ready(function() {
-  // Shows permalink when term name is hovered over
-  $(".glossary-injector").each(function() {
-    var placeholder = $("#" + $(this).data("placeholder-id"));
-    var originalContent = placeholder.html();
-
-    var glossaryDef = $($(this).find(".injector-def")[0]).html();
-
-    $(this).mouseenter(function() {
-      placeholder.html(glossaryDef);
-    }).mouseleave(function(){
-      placeholder.html(originalContent);
-    });
-  });
-});