Remove read_n and read_field from Utils.hpp
Remove read_n and read_field from Utils.hpp

They have been superseded by IStream and Extractor.

Fixes #783.

Sciumo/PDAL,mtCarto/PDAL,mpgerlek/PDAL-old,mpgerlek/PDAL-old,jwomeara/PDAL,boundlessgeo/PDAL,lucadelu/PDAL,radiantbluetechnologies/PDAL,boundlessgeo/PDAL,jwomeara/PDAL,boundlessgeo/PDAL,Sciumo/PDAL,radiantbluetechnologies/PDAL,Sciumo/PDAL,jwomeara/PDAL,DougFirErickson/PDAL,radiantbluetechnologies/PDAL,jwomeara/PDAL,mtCarto/PDAL,DougFirErickson/PDAL,radiantbluetechnologies/PDAL,boundlessgeo/PDAL,lucadelu/PDAL,mtCarto/PDAL,DougFirErickson/PDAL,mpgerlek/PDAL-old,lucadelu/PDAL,mpgerlek/PDAL-old,mtCarto/PDAL,lucadelu/PDAL,Sciumo/PDAL,DougFirErickson/PDAL