Do not create keep_arounds when importing

Today, when processing Note/MergeRequestDiff/MergeRequest/DiffNote,
we would create keep arounds in a transactaion when importing.

This does not make sense, as this repository is somehow a replica
of another one and we cannot guarantee anything about this repository,
also this increases the repository fragmentation while creating them.

app/models/diff_note.rb

@@ -22,7 +22,7 @@ class DiffNote < Note
   validate :verify_supported
 
   before_validation :set_line_code, if: :on_text?
-  after_save :keep_around_commits
+  after_save :keep_around_commits, unless: :importing?
   after_commit :create_diff_file, on: :create
 
   def discussion_class(*)
@@ -104,7 +104,7 @@ class DiffNote < Note
   end
 
   def should_create_diff_file?
-    on_text? && note_diff_file.nil? && start_of_discussion?
+    false && on_text? && note_diff_file.nil? && start_of_discussion?
   end
 
   def fetch_diff_file

app/models/merge_request.rb

@@ -242,7 +242,7 @@ class MergeRequest < ApplicationRecord
 
   ignore_column :state, remove_with: '12.7', remove_after: '2019-12-22'
 
-  after_save :keep_around_commit
+  after_save :keep_around_commit, unless: :importing?
 
   alias_attribute :project, :target_project
   alias_attribute :project_id, :target_project_id

app/models/merge_request_diff.rb

@@ -164,7 +164,7 @@ class MergeRequestDiff < ApplicationRecord
     # hooks that run when an attribute was changed are run twice.
     reset
 
-    keep_around_commits
+    keep_around_commits unless importing?
   end
 
   def set_as_latest_diff

app/models/note.rb

@@ -155,7 +155,7 @@ class Note < ApplicationRecord
   after_initialize :ensure_discussion_id
   before_validation :nullify_blank_type, :nullify_blank_line_code
   before_validation :set_discussion_id, on: :create
-  after_save :keep_around_commit, if: :for_project_noteable?
+  after_save :keep_around_commit, if: :for_project_noteable?, unless: :importing?
   after_save :expire_etag_cache
   after_save :touch_noteable
   after_destroy :expire_etag_cache