aliases/implications: remove dead approving/updating code.

Remove the edit, update, and approve endpoints for tag aliases and
implications. These have been useless since individual alias and
implication requests were removed. Aliases and implications could only
be edited or approved if they were in the pending state, which is no
longer possible.

Also remove unused new alias/implication request forms.

app/models/tag_relationship.rb

@@ -66,14 +66,7 @@ class TagRelationship < ApplicationRecord
   end
 
   def deletable_by?(user)
-    return true if user.is_admin?
-    return true if is_pending? && user.is_builder?
-    return true if is_pending? && user.id == creator_id
-    return false
-  end
-
-  def editable_by?(user)
-    deletable_by?(user)
+    user.is_admin?
   end
 
   def reject!(update_topic: true)