Refactor commands to remove "require cmd/help"

Library/Homebrew/brew.rb

Library/Homebrew/cmd/--cache.rb

Library/Homebrew/cmd/fetch.rb

Library/Homebrew/cmd/help.rb

Library/Homebrew/cmd/install.rb

Library/Homebrew/cmd/link.rb

Library/Homebrew/cmd/style.rb

Library/Homebrew/cmd/switch.rb

Library/Homebrew/cmd/upgrade.rb

Library/Homebrew/dev-cmd/audit.rb

Library/Homebrew/fetch.rb

Library/Homebrew/formulary.rb

Library/Homebrew/help.rb

Library/Homebrew/install.rb

Library/Homebrew/style.rb

Library/Homebrew/test/cmd/style_spec.rb

docs/Manpage.md

manpages/brew-cask.1

manpages/brew.1