BUG-614: sal-common-impl does not use xtend

This is a cleanup of sal-common-impl component -- it no longer uses
xtend, so there is no reason to depend on the maven plugin nor the
support library.

Change-Id: Ifa5d9934997f8f4d6a9d4f1b9db5f251b421713c
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-614: sal-common-impl does not use xtend"