MaterializedView does not delete correctly documents

[estebgonza]

When a Materialized View triggers a deleteDocument, the accumulators are updated correctly but not the "_id".

Reproduction:

With collection: [{country: 'France'}]

Create a MV with a groupBy on country: the view contains an 'France' entry.
Trigger addDocument on the mv: mv.addDocument({country: 'Switzerland'}).
The MV contains: [{country: 'France'}, {country: 'Switzerland'}]
Trigger deleteDocument: mv.deleteDocument({country: 'Switzerland'})
⚠️ The MV still contains: [{country: 'France'}, {country: 'Switzerland'}] instead of [{country: 'France'}].