[cloud_firestore_web] Remove unit test that was only testing dart-lang.

[ditman]

Description

The problematic test was attempting to coerce a wrong type into a function call, and that causes problems in environments where linting is more strict. Remove the test, since it's not actually testing our functionality, but dart-lang's.

Related Issues

Fixes #1991

Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
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Breaking Change

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[harryterkelsen]

LGTM

[ditman]

I'll merge and publish as soon as CI goes green. Thanks @hterkelsen for the quick review!