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/index.html.erb

@@ -39,8 +39,6 @@
   <%= render "posts/partials/index/posts", :post_set => @post_set %>
 <% end %>
 
-<%= post_search_count_js %>
-
 <div id="saved-searches-nav">
   <%= render "saved_searches/interface" %>
 </div>
@@ -51,6 +49,14 @@
   <%= render "posts/partials/common/secondary_links" %>
 <% end %>
 
+<% if post_search_counts_enabled? && @post_set.query.is_simple_tag? && @post_set.current_page == 1 %>
+  <% if @post_set.post_count == 0 %>
+    <%= missed_post_search_count_js %>
+  <% else %>
+    <%= post_search_count_js %>
+  <% end %>
+<% end %>
+
 <% content_for(:html_header) do %>
   <%= render "posts/partials/index/seo_meta_tags" %>
 <% end %>

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 %>