fix: [stix2 export] Reverted the email object attribute 'from' export as observable object
fix: [stix2 export] Reverted the email object attribute 'from' export as observable object

- From-ref is always a single value, we cannot use
  a list of references

SteveClement/MISP,SteveClement/MISP,MISP/MISP,MISP/MISP,SteveClement/MISP,MISP/MISP,SteveClement/MISP,MISP/MISP,MISP/MISP,SteveClement/MISP