Remove outdated project from README.md

[yangsfang]

Per simc/logger_flutter#16 the logger_flutter project is no longer maintained. It has become very outdated and not usable with the latest logger.

[Bungeefan]

Just to mention it once:
Originally there were ideas to also maintain flutter_logger, however, we had no access to the pub.dev package.
And as far as I know @Oliinyk-Volodymyr published a fork of it on pub.dev, but it seems that this has ended as well: https://pub.dev/packages/logger_flutter_plus

Therefore, I am fine with removing the passage from the README, thanks for your PR!

[yjlin0224]

I found a replacement https://pub.dev/packages/logger_screen to logger_flutter_plus and flutter_logger