Use DC2 source for ZAM relations in vsup_ifis
Use DC2 source for ZAM relations in vsup_ifis

- Replaced VEMA with DC2.
- DC2 has unique ID for all relations, handle it as EXT_ID
  column directly.
- Keep VEMA differences as coments just to be sure.
- Renamed variables to mention DC2 instead of VEMA.

CESNET/perun-services,zlamalp/perun-services,zlamalp/perun-services,CESNET/perun-services,zlamalp/perun-services,CESNET/perun-services,zlamalp/perun-services,CESNET/perun-services