Remove deprecated info from .env.example and README

[dasanra]

What it solves

There were some legacy information in .env.example and README that was causing confusion to some devs trying to run the interface

How this PR fixes it

It updates the docs to be aligned with latest changes for unified version

[github-actions]

CLA Assistant Lite All Contributors have signed the CLA.

[github-actions]

ESLint Summary View Full Report

Annotations are provided inline on the Files Changed tab. You can also see all annotations that were generated on the annotations page.

Type	Occurrences	Fixable
Errors	0	0
Warnings	0	0
Ignored	0	N/A

• Result: ✅ success
• Annotations: 0 total

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^{Report generated by eslint-plus-action}

[github-actions]

Deployment links

🟠 Safe Rinkeby	⚪ Safe Mainnet	🟣 Safe Polygon	🟡 Safe BSC	⚫ Safe Arbitrum	🟢 Safe xDai

[coveralls]

Pull Request Test Coverage Report for Build 1495407728

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 31.878%

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Totals
Change from base Build 1495261950:	0.0%
Covered Lines:	2983
Relevant Lines:	8353

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💛 - Coveralls

[github-actions]

E2E Tests Failed
Check the results here: https://github.com/gnosis/safe-react-e2e-tests/actions/runs/1495443523

Failed tests:

• ❌ Safe Apps List Safe Apps List

[katspaugh]

Nice, thanks @dasanra!