man: Remove [] from command synopsis

Library/Homebrew/dev-cmd/audit.rb

Library/Homebrew/dev-cmd/bottle.rb

Library/Homebrew/dev-cmd/bump-formula-pr.rb

Library/Homebrew/dev-cmd/create.rb

Library/Homebrew/dev-cmd/irb.rb

Library/Homebrew/dev-cmd/linkage.rb

Library/Homebrew/dev-cmd/man.rb

Library/Homebrew/dev-cmd/pull.rb

Library/Homebrew/dev-cmd/release-notes.rb

Library/Homebrew/dev-cmd/tests.rb

Library/Homebrew/dev-cmd/update-test.rb

docs/Manpage.md

manpages/brew.1