Keep Orderer.FileLedger.Prefix in orderer localconfig
Keep Orderer.FileLedger.Prefix in orderer localconfig

This setting is no longer supported but without it in the localconfig,
existing orderer YAML files won't work and the orderer won't start.

FAB-18101 #done

Signed-off-by: Will Lahti <f19a2779710675aad3df5c81e4ecfde11707e3aa@us.ibm.com>

manish-sethi/fabric,stemlending/fabric,stemlending/fabric,stemlending/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,hyperledger/fabric,jimthematrix/fabric,hyperledger/fabric,manish-sethi/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,jimthematrix/fabric,stemlending/fabric,manish-sethi/fabric-sidedb