chore(doc): clean up deprecated config reference

[emilyrohrbough]

This config value was removed in Cypress 7.0.0 - https://docs.cypress.io/guides/references/changelog#7-0-0. Remove from manual installations instructions.

User facing changelog

n/a

Additional details

PR Tasks

• [n/a] Have tests been added/updated?
• [n/a] Has the original issue (or this PR, if no issue exists) been tagged with a release in ZenHub? (user-facing changes only)
• [n/a] Has a PR for user-facing changes been opened in cypress-documentation?
• [n/a] Have API changes been updated in the type definitions?
• [n/a] Have new configuration options been added to the cypress.schema.json?

[cypress-bot]

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[cypress]

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Test summary

19339 • 0 • 218 • 0 • 2

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Run details

Project	cypress
Status	Passed
Commit	0f1a562
Started	Mar 16, 2022 7:08 PM
Ended	Mar 16, 2022 7:19 PM
Duration	11:30 💡
OS	Linux Debian - 10.10
Browser	Multiple

View run in Cypress Dashboard ➡️

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Flakiness

	reporter.hooks.spec.js		1
1	hooks > can rerun without timeout error leaking into next run (due to run restart)
	cypress/source_map_utils_spec.js		1
1	driver/src/cypress/source_map_utils > .extractSourceMap > is performant with multiple source map comments in file

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