posts/index: fix search count tracking.

* Eliminate "&ms=1" url param.
* Only track simple single-tag searches (not multi-tag searches,
  metatags, negated tags, etc).

app/views/posts/partials/common/_search.html.erb

@@ -11,6 +11,5 @@
     <% end %>
     <%= text_field_tag("tags", tags, :id => tags_dom_id, :"data-shortcut" => "q", :"data-autocomplete" => "tag-query") %>
     <button id="search-box-submit" type="submit"><i class="fas fa-search"></i></button>
-    <%= hidden_field_tag "ms", "1" %>
   <% end %>
 </section>