Drop Resque\Logger class

[pprkut]

This removes the internal PSR-3 logger. Now, if no custom logger is set up in the APP_INCLUDE, logging is disabled.

I think by now everyone is using PSR-3 and there's no need to continue shipping our own logger. Dropping it allows us to support a wider range of psr/log, which provides projects the freedom to choose the best version for them. Should also help a bit with PHP 8 compatibility (since latest monolog no longer supports PHP 7)