Configuration documentation: remove deprecated/wrong [core]max_reschedules entry
Configuration documentation: remove deprecated/wrong [core]max_reschedules entry

The configration doc contains entry on `[core]max_reschedules`,
which is not only deprecated (in favor of `[worker]max_reschedules`)
but also wrong: the correct (but deprecated) config key is
`[core]worker-max-reschedules`.
Better get rid of this all together and just keep `[worker]max_reschedules`

soxofaan/luigi,soxofaan/luigi,soxofaan/luigi,soxofaan/luigi