chore: remove mongodb example

[SimenB]

Summary

We're getting this error on (Circle) CI:

Starting the MongoMemoryServer Instance failed, enable debug log for more information. Error:
 StdoutInstanceError: Instance failed to start because a library is missing or cannot be opened: "libcrypto.so.1.1"
    at MongoInstance.checkErrorInLine (/home/circleci/jest/node_modules/mongodb-memory-server-core/lib/util/MongoInstance.js:357:62)
    at MongoInstance.stderrHandler (/home/circleci/jest/node_modules/mongodb-memory-server-core/lib/util/MongoInstance.js:287:14)
    at Socket.emit (node:events:513:28)
    at addChunk (node:internal/streams/readable:315:12)
    at readableAddChunk (node:internal/streams/readable:289:9)
    at Socket.Readable.push (node:internal/streams/readable:228:10)
    at Pipe.onStreamRead (node:internal/stream_base_commons:190:23)
Error: Instance failed to start because a library is missing or cannot be opened: "libcrypto.so.1.1"
    at MongoInstance.checkErrorInLine (/home/circleci/jest/node_modules/mongodb-memory-server-core/lib/util/MongoInstance.js:357:62)
    at MongoInstance.stderrHandler (/home/circleci/jest/node_modules/mongodb-memory-server-core/lib/util/MongoInstance.js:287:14)
    at Socket.emit (node:events:513:28)
    at addChunk (node:internal/streams/readable:315:12)
    at readableAddChunk (node:internal/streams/readable:289:9)
    at Socket.Readable.push (node:internal/streams/readable:228:10)
    at Pipe.onStreamRead (node:internal/stream_base_commons:190:23)

Exited with code exit status 1

Not sure if it helps updating, but probably doesn't hurt.

That didn't help, so I'll just remove the entire example. I don't think it provides much value to us (and its binary nature has caused issues for us before), and a preset is documented: https://jestjs.io/docs/mongodb

Test plan

Green CI

[github-actions]

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