Eliminate the use of xtend in md-sal/sal-dom-broker

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

opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/sal/dom/broker/BrokerConfigActivator.xtend
opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/sal/dom/broker/BrokerImpl.xtend
opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/sal/dom/broker/ConsumerContextImpl.xtend
opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/sal/dom/broker/impl/DataReaderRouter.xtend
opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/sal/dom/broker/impl/HashMapDataStore.xtend
opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/sal/dom/broker/MountPointManagerImpl.xtend
opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/sal/dom/broker/osgi/ProxyFactory.xtend
opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/sal/dom/broker/ProviderContextImpl.xtend
opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/sal/dom/broker/util/YangDataOperations.xtend

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