tmf remote: clean up RemoteSystemProxy class

tmf remote: clean up RemoteSystemProxy class

Remove pass-through methods to IRemoteConnection instance. Users
can get the connection from the proxy and act directly on it.

This avoids duplication of methods.

Change-Id: I0cdd8a9ceb698ebdb6f7404f07d449e5bdaa7bee
Signed-off-by: Bernd Hufmann <Bernd.Hufmann@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/44877
Reviewed-by: Hudson CI
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>