tags: exclude deprecated tags from related tags list.

Don't show deprecated tags in the related tags or translated tags lists
when editing a post. It doesn't make sense to recommended adding tags
that can't be added to the post.

app/models/tag.rb

@@ -22,6 +22,8 @@ class Tag < ApplicationRecord
 
   scope :empty, -> { where("tags.post_count <= 0") }
   scope :nonempty, -> { where("tags.post_count > 0") }
+  scope :deprecated, -> { where(is_deprecated: true) }
+  scope :undeprecated, -> { where(is_deprecated: false) }
 
   module ApiMethods
     def to_legacy_json

app/models/wiki_page.rb

@@ -206,7 +206,7 @@ class WikiPage < ApplicationRecord
 
   def tags
     titles = DText.parse_wiki_titles(body).uniq
-    tags = Tag.nonempty.where(name: titles).pluck(:name)
+    tags = Tag.nonempty.undeprecated.where(name: titles).pluck(:name)
     tags += TagAlias.active.where(antecedent_name: titles).pluck(:antecedent_name)
     TagAlias.to_aliased(titles & tags)
   end