Removed dead code that is not being built

Dead code that is not being built (and hasn't been for a while) makes it extremely hard to fix version reliably and verify they are fixed. Therefore, the code should be removed (if removed in error it can always be restored).

Specific cases are:

opendaylight/distribution/p2site/
opendaylight/md-sal/clustered-data-store/
opendaylight/md-sal/remoterpc-routingtable/
opendaylight/md-sal/sal-remoterpc-connector/
opendaylight/md-sal/sal-data-api
opendaylight/md-sal/sal-dom-demo
opendaylight/md-sal/test/sal-rest-connector-it/
opendaylight/northboundtest/unit_test_suite/
opendaylight/samples/clustersession/
opendaylight/web/brandfragment/

Note: opendaylight/northbound/java-client/ is also a similarly unloved
component, but appears to be used in the doc profile and thus requires more
investigation.