Remove EE-specific code from DiscussionNote

app/models/concerns/noteable.rb

@@ -23,7 +23,7 @@ module Noteable
   end
 
   def supports_discussions?
-    DiscussionNote::NOTEABLE_TYPES.include?(base_class_name)
+    DiscussionNote.noteable_types.include?(base_class_name)
   end
 
   def discussions_rendered_on_frontend?

app/models/diff_note.rb

@@ -8,12 +8,14 @@ class DiffNote < Note
   include DiffPositionableNote
   include Gitlab::Utils::StrongMemoize
 
-  NOTEABLE_TYPES = %w(MergeRequest Commit).freeze
+  def self.noteable_types
+    %w(MergeRequest Commit)
+  end
 
   validates :original_position, presence: true
   validates :position, presence: true
   validates :line_code, presence: true, line_code: true, if: :on_text?
-  validates :noteable_type, inclusion: { in: NOTEABLE_TYPES }
+  validates :noteable_type, inclusion: { in: noteable_types }
   validate :positions_complete
   validate :verify_supported
   validate :diff_refs_match_commit, if: :for_commit?

app/models/discussion_note.rb

@@ -5,9 +5,11 @@
 # A note of this type can be resolvable.
 class DiscussionNote < Note
   # Names of all implementers of `Noteable` that support discussions.
-  NOTEABLE_TYPES = %w(MergeRequest Issue Commit Snippet).freeze
+  def self.noteable_types
+    %w(MergeRequest Issue Commit Snippet)
+  end
 
-  validates :noteable_type, inclusion: { in: NOTEABLE_TYPES }
+  validates :noteable_type, inclusion: { in: noteable_types }
 
   def discussion_class(*)
     Discussion