[Docs] mapReduce removal is not listed as breaking change in mongoose 7.x

[arieltorti]

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Issue

Currently, the migration guide from 6.x to 7.x (https://mongoosejs.com/docs/migrating_to_7.html) doesn't mention the removal of mapReduce made in a4eb9c9.

I'm aware that MongoDB deprecated mapReduce in 5.x but mongoose 7.x documentation says it works with Mongo 4.x:

From: https://mongoosejs.com/docs/compatibility.html

Should we update the breaking changes documentation to also include the removal of mapReduce ?