Remove legacy query to find job artifacts that have been synced

This commit removes the legacy queries to find job artifacts
that have been synced since we made Foreign Data Wrapper (FDW)
a hard requirement for Geo on GitLab 12.0.

ee/app/finders/geo/job_artifact_registry_finder.rb

@@ -7,7 +7,7 @@ module Geo
     end
 
     def count_synced
-      job_artifacts_synced.count
+      registries_for_job_artifacts.merge(Geo::JobArtifactRegistry.synced).count
     end
 
     def count_failed
@@ -112,14 +112,6 @@ module Geo
       end
     end
 
-    def job_artifacts_synced
-      if use_legacy_queries_for_selective_sync?
-        legacy_finder.job_artifacts_synced
-      else
-        registries_for_job_artifacts.merge(Geo::JobArtifactRegistry.synced)
-      end
-    end
-
     def job_artifacts_failed
       if use_legacy_queries_for_selective_sync?
         legacy_finder.job_artifacts_failed

ee/app/finders/geo/legacy_job_artifact_registry_finder.rb

@@ -6,14 +6,6 @@ module Geo
       current_node.job_artifacts.syncable
     end
 
-    def job_artifacts_synced
-      legacy_inner_join_registry_ids(
-        syncable,
-        Geo::JobArtifactRegistry.synced.pluck_artifact_key,
-        Ci::JobArtifact
-      )
-    end
-
     def job_artifacts_failed
       legacy_inner_join_registry_ids(
         syncable,