chore: remove numTestsKeptInMemory from cypress config because default behaviour is better

[HendrikThePendric]

No JIRA issue available,

Having numTestsKeptInMemory set to a low number can make local debugging using cy:opendifficult. Normally you can hover over steps to see the state of the DOM in each one. However, when the number of tests in the current test file exceed the value of numTestsKeptInMemory, you well start seeing message saying The snapshot is missing. Displaying current state of the DOM for the first tests in the file.

After inspecting the Cypress docs, it turns out that the default behaviour is actually what we want:

The number of tests for which snapshots and command data are kept in memory. numTestsKeptInMemory is set to 50 by default during cypress open and set to 0 by default during cypress run. Reduce this number if you are experiencing high memory consumption in your browser during a test run.

This way we should not encounter out-of-memory errors on CI (which uses cypress run), and we should be able to visually debug tests locally using cypress open.

Also see this Slack thread

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