change post nav setting to post nav js setting

app/assets/javascripts/posts.js

@@ -7,8 +7,9 @@
     this.initialize_titles();
 
     if ($("#c-posts").length) {
-      this.initialize_shortcuts();
-      this.initialize_nav_help_link();
+      if (Danbooru.meta("enable-js-navigation") === "true") {
+        this.initialize_shortcuts();
+      }
     }
 
     if ($("#c-posts").length && $("#a-index").length) {
@@ -125,9 +126,6 @@
       e.preventDefault();
     });
   }
-  
-  Danbooru.Post.initialize_nav_help_link = function() {
-  }
 
   Danbooru.Post.initialize_titles = function() {
     $(".post-preview").each(function(i, v) {