fix(046_22_08, 034_05_01): the NGSI-LD Null in a deletion notification and in an update

Two Test Cases that get the NGSI-LD Null wrong.

• 046_22_08: name has three instances in building-multi-instances-attributes (the default one and two datasetIds), and all three are deleted. TS 104-175 clause 10.5.7: a deleted Attribute that needs a datasetId is notified as a JSON object whose value is urn:ngsi-ld:null - one per instance. So name is an Array of three such objects; the TC read it as one object and failed inside Robot (list indices must be integers). It now checks the three instances.
• 034_05_01: expiresAt is removed with the NGSI-LD Null "urn:ngsi-ld:null". TS 104-175 clause 8.4.2: a Fragment member whose value is an NGSI-LD Null deletes the target member. The fixture sent a JSON null, which JSON-LD expansion drops before the update, so the update did nothing.

2 Test Cases. Both fail on develop and pass with this MR.