Remove legacy query to find attachments to sync

This commit removes the legacy queries to find attachments
to sync since we made Foreign Data Wrapper (FDW) a hard
requirement for Geo on GitLab 12.0.

ee/app/finders/geo/attachment_registry_finder.rb

@@ -44,14 +44,7 @@ module Geo
     # @param [Array<Integer>] except_file_ids ids that will be ignored from the query
     # rubocop: disable CodeReuse/ActiveRecord
     def find_unsynced(batch_size:, except_file_ids: [])
-      relation =
-        if use_legacy_queries_for_selective_sync?
-          legacy_finder.attachments_unsynced(except_file_ids: except_file_ids)
-        else
-          attachments_unsynced(except_file_ids: except_file_ids)
-        end
-
-      relation.limit(batch_size)
+      attachments_unsynced(except_file_ids: except_file_ids).limit(batch_size)
     end
     # rubocop: enable CodeReuse/ActiveRecord
 

ee/app/finders/geo/legacy_attachment_registry_finder.rb

@@ -16,16 +16,6 @@ module Geo
       )
     end
 
-    def attachments_unsynced(except_file_ids:)
-      registry_file_ids = Geo::FileRegistry.attachments.pluck_file_key | except_file_ids
-
-      legacy_left_outer_join_registry_ids(
-        syncable,
-        registry_file_ids,
-        Upload
-      )
-    end
-
     private
 
     def attachments

ee/spec/finders/geo/attachment_registry_finder_spec.rb

@@ -503,7 +503,58 @@ describe Geo::AttachmentRegistryFinder, :geo do
       stub_fdw_disabled
     end
 
-    include_examples 'finds all the things'
+    describe '#find_migrated_local' do
+      let!(:upload_1) { create(:upload, model: synced_group) }
+      let!(:upload_2) { create(:upload, model: unsynced_group) }
+      let!(:upload_3) { create(:upload, :issuable_upload, model: synced_project) }
+      let!(:upload_4) { create(:upload, model: unsynced_project) }
+      let!(:upload_5) { create(:upload, model: synced_project) }
+      let!(:upload_remote_1) { create(:upload, :object_storage, model: synced_project) }
+      let!(:upload_remote_2) { create(:upload, :object_storage, model: unsynced_project) }
+
+      before do
+        create(:geo_file_registry, :avatar, file_id: upload_remote_1.id)
+        create(:geo_file_registry, :avatar, file_id: upload_remote_2.id)
+      end
+
+      it 'returns attachments stored remotely and successfully synced locally' do
+        attachments = subject.find_migrated_local(batch_size: 100, except_file_ids: [upload_remote_2.id])
+
+        expect(attachments).to match_ids(upload_remote_1)
+      end
+
+      it 'excludes attachments stored remotely, but not synced yet' do
+        create(:upload, :object_storage, model: synced_group)
+
+        attachments = subject.find_migrated_local(batch_size: 100)
+
+        expect(attachments).to match_ids(upload_remote_1, upload_remote_2)
+      end
+
+      context 'with selective sync by namespace' do
+        before do
+          secondary.update!(selective_sync_type: 'namespaces', namespaces: [synced_group])
+        end
+
+        it 'returns attachments stored remotely and successfully synced locally' do
+          attachments = subject.find_migrated_local(batch_size: 10)
+
+          expect(attachments).to match_ids(upload_remote_1)
+        end
+      end
+
+      context 'with selective sync by shard' do
+        before do
+          secondary.update!(selective_sync_type: 'shards', selective_sync_shards: ['broken'])
+        end
+
+        it 'returns attachments stored remotely and successfully synced locally' do
+          attachments = subject.find_migrated_local(batch_size: 10)
+
+          expect(attachments).to match_ids(upload_remote_2)
+        end
+      end
+    end
 
     describe '#count_syncable' do
       let!(:upload_1) { create(:upload, model: synced_group) }