chore: remove legacy javascripts config option and related code

[lmiller1990]

• Closes N/A

User facing changelog

Removes code relating to undocumented legacy javascripts config option.

Additional details

N/A

How has the user experience changed?

No change

PR Tasks

• Have tests been added/updated?
• Has the original issue or this PR been tagged with a release in ZenHub?
• Has a PR for user-facing changes been opened in cypress-documentation?
• Have API changes been updated in the type definitions?
• Have new configuration options been added to the cypress.schema.json?

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[cypress]

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Test summary

8373 • 2 • 103 • 3 • 4

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Run details

Project	cypress
Status	Failed
Commit	da74782
Started	Sep 16, 2021 12:01 AM
Ended	Sep 16, 2021 12:12 AM
Duration	10:44 💡
OS	Linux Debian - 10.9
Browser	Multiple

View run in Cypress Dashboard ➡️

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Failures

	e2e/focus_blur_spec.js		1
1	intercept blur methods correctly > focus area
	commands/actions/type_spec.js		1
1	... > element

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Flakiness

	cypress/proxy-logging-spec.ts		2
1	Proxy Logging > request logging > fetch log shows resource type, url, method, and status code and has expected snapshots and consoleProps
2	Proxy Logging > request logging > fetch log shows resource type, url, method, and status code and has expected snapshots and consoleProps
	commands/net_stubbing_spec.ts		1
1	network stubbing > intercepting request > can intercept utf-8 request bodies without crashing
	commands/xhr_spec.js		1
1	src/cy/commands/xhr > abort > aborts xhrs currently in flight

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