[cost] remove need for Procdesc.load
[cost] remove need for Procdesc.load

Summary: CFGs do not exist for (all) undefined functions, so it's best to use `Attributes.load` instead of `Procdesc.load` when only attribute fields need to be obtained.

Reviewed By: skcho

Differential Revision: D37646835

fbshipit-source-id: 25e9069204ce6a403c0f00ffacdd64c73eebcd97

facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer