Fix Orion-LD: Remove source from @context

- Testing shows Orion-LD stores source properly WITHOUT defining it in @context
- When defined in @context, it's stored with full URI as key
- Without @context definition, source is stored and returned correctly
- Simulator now creates entities with proper source/mqttTopic fields

simulator.py

@@ -168,7 +168,6 @@ for stype, locs in SENSOR_LOCATIONS.items():
 # Orion-LD ne peut pas résoudre raw.githubusercontent.com — utiliser uri.etsi.org uniquement
 ORION_CONTEXT = [
     "https://uri.etsi.org/ngsi-ld/v1/ngsi-ld-core-context.jsonld",
-    {"source": "https://uri.fiware.org/ngsi-ld/default-context/source"}
 ]
 
 # Mapping sensor type → Smart Data Model type NGSI-LD