Refactor legacy finder to find mismatch registries

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

ee/app/finders/geo/legacy_project_registry_mismatch_finder.rb

@@ -22,30 +22,16 @@ module Geo
     end
 
     def execute
-      if selective_sync?
-        mismatch_registries_for_selective_sync
-      else
-        mismatch_registries
-      end
-    end
-
-    private
-
-    attr_reader :type
-
-    def mismatch_registries
-      Geo::ProjectRegistry.mismatch(type)
-    end
-
-    # rubocop: disable CodeReuse/ActiveRecord
-    def mismatch_registries_for_selective_sync
       legacy_inner_join_registry_ids(
-        mismatch_registries,
-        current_node.projects.pluck(:id),
+        Geo::ProjectRegistry.mismatch(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/spec/finders/geo/legacy_project_registry_mismatch_finder_spec.rb

@@ -3,8 +3,6 @@
 require 'spec_helper'
 
 describe Geo::LegacyProjectRegistryMismatchFinder, :geo do
-  include EE::GeoHelpers
-
   describe '#execute' do
     let(:node) { create(:geo_node) }
     let(:group_1) { create(:group) }
@@ -22,7 +20,6 @@ describe Geo::LegacyProjectRegistryMismatchFinder, :geo do
     let!(:registry_repository_mismatch_broken_shard) { create(:geo_project_registry, :repository_checksum_mismatch, :wiki_verified, project: project_5) }
     let!(:registry_verified) { create(:geo_project_registry, :repository_verified, :wiki_verified) }
 
-    shared_examples 'finds mismatch registries' do
     context 'with repository type' do
       subject { described_class.new(current_node: node, type: :repository) }
 
@@ -101,23 +98,4 @@ describe Geo::LegacyProjectRegistryMismatchFinder, :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 mismatch registries'
-    end
-
-    context 'Legacy' do
-      before do
-        stub_fdw_disabled
-      end
-
-      include_examples 'finds mismatch registries'
-    end
-  end
 end