Remove deprecation of withGracefulShutdownHandler if compiler < 6#194

FranzBusch merged 1 commit intoswift-server:mainswift-server/swift-service-lifecycle:mainfrom

hamzahrmalik:dont_deprecate_withGracefulShutdownHandler_in_older_swifthamzahrmalik/swift-service-lifecycle:dont_deprecate_withGracefulShutdownHandler_in_older_swiftCopy head branch name to clipboard