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>

app/views/posts/partials/index/_seo_meta_tags.html.erb

@@ -10,8 +10,6 @@
   <% atom_feed_tag "Posts: #{@post_set.tag_string}", posts_url(tags: @post_set.tag_string, format: :atom) %>
 <% end %>
 
-<%= missed_post_search_count_js %>
-
 <% if @post_set.hide_from_crawler? %>
   <meta name="robots" content="nofollow,noindex">
 <% end %>