Drop non-atomic collection updates

[alcaeus]

Feature Request

Q	A
New Feature	yes
RFC	no
BC Break	most likely

Summary

With MongoDB 3.6, arrayFilters was introduced to allow modifying arrays in documents with more control: previously, only a single $ operator could be used, so updates to nested arrays were not possible. With arrayFilters, we can use multiple operators, meaning that we can now handle all collection updates with atomic strategies, not only those to root-level collections.