Remove legacy query to find synced LFS objects

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

ee/app/finders/geo/legacy_lfs_object_registry_finder.rb

@@ -6,14 +6,6 @@ module Geo
       current_node.lfs_objects.syncable
     end
 
-    def lfs_objects_synced
-      legacy_inner_join_registry_ids(
-        syncable,
-        Geo::FileRegistry.lfs_objects.synced.pluck_file_key,
-        LfsObject
-      )
-    end
-
     def lfs_objects_failed
       legacy_inner_join_registry_ids(
         syncable,

ee/app/finders/geo/lfs_object_registry_finder.rb

@@ -110,11 +110,7 @@ module Geo
     end
 
     def lfs_objects_synced
-      if use_legacy_queries_for_selective_sync?
-        legacy_finder.lfs_objects_synced
-      else
-        fdw_geo_node.lfs_objects.synced
-      end
+      fdw_geo_node.lfs_objects.synced
     end
 
     def lfs_objects_failed