[Refactor] TargetIntegrator#native_targets_to_integrate

lib/cocoapods/installer/user_project_integrator/target_integrator.rb

@@ -186,13 +186,11 @@ module Pod
         #
         def native_targets_to_integrate
           unless @native_targets_to_integrate
-            @native_targets_to_integrate = native_targets.reject do |native_target|
-              native_target.frameworks_build_phase.files.any? do |build_file|
-                file_ref = build_file.file_ref
-                file_ref &&
-                  file_ref.isa == 'PBXFileReference' &&
+            @native_targets_to_integrate = native_targets.select do |native_target|
+              links_target = native_target.frameworks_build_phase.files_references.any? do |file_ref|
                 file_ref.display_name == target.product_name
               end
+              !links_target
             end
           end
           @native_targets_to_integrate