slapos.promise: cleanup and remove promise history and statistics from slapos.core

Promise history should be generated in slapos.toolbox https://lab.nexedi.com/nexedi/slapos.toolbox/-/tree/master/slapos/monitor

Statistics and monitor state data are also moved to slapos.toolbox. See changes https://lab.nexedi.com/nexedi/slapos.toolbox/-/merge_requests/166