[MEDI] Use the AutoGenerated Guid key feature added recently by MEVD

[adamsitnik]

We don't need to do this anymore:

extensions/src/Libraries/Microsoft.Extensions.DataIngestion/Writers/VectorStoreWriter.cs

Line 81 in 8b00e5b

var key = Guid.NewGuid();

cc @roji

[adamsitnik]

Fixed by #7423