fix no autoremove suggestion typo

[apainintheneck]

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This currently suggests setting an environment variable that is different than the one we end up checking so I've updated the warning so now things match. If the goal was to have the name in the warning, the environment variable checking logic could be updated. I have no personal preference.

$ brew irb
==> Interactive Homebrew Shell
Example commands available with: `brew irb --examples`
brew(main):001:0> ENV["HOMEBREW_NO_AUTO_REMOVE"] = "1"
=> "1"
brew(main):002:0> Homebrew::EnvConfig.no_autoremove?
=> false
brew(main):003:0> ENV["HOMEBREW_NO_AUTOREMOVE"] = "1"
=> "1"
brew(main):004:0> Homebrew::EnvConfig.no_autoremove?
=> true

[ZhongRuoyu]

Thanks for catching this!

[MikeMcQuaid]

@apainintheneck Doh, thanks for catching this! ❤️