Eliminate the use of xtend in md-sal/forwardingrules-manager

All eleven xtend files should be trivial to write in Java, reducing both compile-time and run-time overhead.

opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/AbstractTransaction.xtend
opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/flow/FlowCommitHandler.xtend
opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/flow/FlowProvider.xtend
opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/flow/FlowTransaction.xtend
opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/FRMActivator.xtend
opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/group/GroupCommitHandler.xtend
opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/group/GroupProvider.xtend
opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/group/GroupTransaction.xtend
opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/meter/MeterCommitHandler.xtend
opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/meter/MeterProvider.xtend
opendaylight/md-sal/forwardingrules-manager/src/main/java/org/opendaylight/controller/frm/meter/MeterTransaction.xtend

Also be sure to drop the plugin/lib dependency from pom.xml.