Refactor legacy finder to find registries where sync has failed

These changes use the new finder when FDW is enabled without selective
sync to avoid code duplication.

ee/app/finders/geo/legacy_project_registry_sync_failed_finder.rb

@@ -2,7 +2,7 @@
 
 # Finder for retrieving project registries that synchronization have
 # failed scoped to a type (repository or wiki) using cross-database
-# joins for selective sync.
+# joins.
 #
 # Basic usage:
 #
@@ -22,30 +22,16 @@ module Geo
     end
 
     def execute
-      if selective_sync?
-        failed_registries_for_selective_sync
-      else
-        failed_registries
-      end
-    end
-
-    private
-
-    attr_reader :type
-
-    def failed_registries
-      Geo::ProjectRegistry.sync_failed(type)
-    end
-
-    # rubocop: disable CodeReuse/ActiveRecord
-    def failed_registries_for_selective_sync
       legacy_inner_join_registry_ids(
-        failed_registries,
-        current_node.projects.pluck(:id),
+        Geo::ProjectRegistry.sync_failed(type),
+        current_node.projects.pluck_primary_key,
         Geo::ProjectRegistry,
         foreign_key: :project_id
       )
     end
-    # rubocop: enable CodeReuse/ActiveRecord
+
+    private
+
+    attr_reader :type
   end
 end

ee/app/finders/geo/project_registry_finder.rb

@@ -182,10 +182,10 @@ module Geo
     end
 
     def finder_klass_for_failed_registries
-      if Gitlab::Geo::Fdw.enabled_for_selective_sync?
-        Geo::ProjectRegistrySyncFailedFinder
-      else
+      if !Gitlab::Geo::Fdw.enabled? || use_legacy_queries_for_selective_sync?
         Geo::LegacyProjectRegistrySyncFailedFinder
+      else
+        Geo::ProjectRegistrySyncFailedFinder
       end
     end
 

ee/spec/finders/geo/legacy_project_registry_sync_failed_finder_spec.rb

@@ -22,7 +22,10 @@ describe Geo::LegacyProjectRegistrySyncFailedFinder, :geo do
     let!(:registry_repository_failed_broken_shard) { create(:geo_project_registry, :synced, :repository_sync_failed, project: project_5) }
     let!(:registry_synced) { create(:geo_project_registry, :synced) }
 
-    shared_examples 'finds failed registries' do
+    before do
+      stub_fdw_disabled
+    end
+
     context 'with repository type' do
       subject { described_class.new(current_node: node, type: :repository) }
 
@@ -101,23 +104,4 @@ describe Geo::LegacyProjectRegistrySyncFailedFinder, :geo do
       end
     end
   end
-
-    # Disable transactions via :delete method because a foreign table
-    # can't see changes inside a transaction of a different connection.
-    context 'FDW', :delete do
-      before do
-        skip('FDW is not configured') unless Gitlab::Geo::Fdw.enabled?
-      end
-
-      include_examples 'finds failed registries'
-    end
-
-    context 'Legacy' do
-      before do
-        stub_fdw_disabled
-      end
-
-      include_examples 'finds failed registries'
-    end
-  end
 end