migration from EDProducer to stream::EDProducer (PixelVertexProducer)

as reported by @fwyzard
https://docs.google.com/spreadsheets/d/1D9khDvOl05WEbznsUPCusEbrHeep9hh8cXedMXX09Gc/edit#gid=0
there are modules used @HLT which still need to be migrated and be multithread safe

this is the migration of the module PixelVertexProducer