chore: Remove decaffeinate tasks and some other leftover references to coffeescript

[jennifer-shehane]

Since CoffeeScript is no longer part of the repo per #2690, the decaffeinate tasks and tests surrounding them can be removed.

User Changelog

N/A

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[cypress]

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Test summary

9197 • 0 • 118 • 3 • 1

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Run details

Project	cypress
Status	Passed
Commit	f16cb6b
Started	Jan 15, 2021 6:00 AM
Ended	Jan 15, 2021 6:15 AM
Duration	14:14 💡
OS	Linux Debian - 10.5
Browser	Multiple

View run in Cypress Dashboard ➡️

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Flakiness

	cypress/integration/retries.ui.spec.js		1
1	runner/cypress retries.ui.spec > opens attempt on each attempt failure for the screenshot, and closes after test passes

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[jennifer-shehane]

I've been told that there are still some tests leftover that are in CoffeeScript, so I'm going to try to convert those first before asking for review on this.

[jennifer-shehane]

Replaced by #14586