remove unnecessary Jekyll::Page constant (#6770)

Merge pull request 6770

lib/jekyll/page.rb

@@ -11,8 +11,6 @@ module Jekyll
 
     alias_method :extname, :ext
 
-    FORWARD_SLASH = "/".freeze
-
     # Attributes for Liquid templates
     ATTRIBUTES_FOR_LIQUID = %w(
       content
@@ -64,11 +62,11 @@ module Jekyll
     #
     # Returns the String destination directory.
     def dir
-      if url.end_with?(FORWARD_SLASH)
+      if url.end_with?("/")
         url
       else
         url_dir = File.dirname(url)
-        url_dir.end_with?(FORWARD_SLASH) ? url_dir : "#{url_dir}/"
+        url_dir.end_with?("/") ? url_dir : "#{url_dir}/"
       end
     end