AT:

• the missing entities check is removed
• the import is not adding instances multiple times

Context:
Currently, to prevent entities (e.g. variable instances) from being imported several times, Elasticsearch is queried to check if the given entities have already been imported. The idea is to only import new entities to Elasticsearch.
However, this check is not needed anymore, since when addind new instances to Elasticsearch we do that check on the fly when adding them (have a look at Elasticsearch upsert)