remove Cask::Config.explicit_s

[hyuraku]

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solved # todo in https://github.com/Homebrew/brew/blob/4.4.3/Library/Homebrew/cask/config.rb#L195 because of Homebrew/homebrew-bundle#1476

[ZhongRuoyu]

Thanks!

This also needs to be removed:

brew/Library/Homebrew/test/cask/config_spec.rb

Lines 75 to 77 in 6469a24

	it "returns string of explicit config keys and values" do
	expect(config.explicit_s).to eq('appdir: "/explicit/path/to/apps", language: "zh-TW,en"')
	end