netlist generation: remove option "replace IC and U ref by X" (broken option).
All component refs are now prefixed by the Spice_Primitive field value.
Therefore the netlist used by Kicad ngsipce simulator and the spice netlist generated from dialog are the same.
(note: like previously, forbidden chars like ( and ) are replaced by _ in netnames)
This commit creates more issues than resolves. It could happen that
there are components with different reference types (e.g. U1 and IC1)
that would be later converted to X1, causing a conflict.
jean-pierre charras
Maciej Suminski