libxaw: drop libxp and printproto from DEPENDS

* it was removed from oe-core
  http://git.openembedded.org/openembedded-core/commit/?id=5b3748d463a6666c0d8e2624092619da8d8e6328


* there should be --disable-xprint/--without-xprint too, but it looks
  like all support for xprint was removed from libxaw already

  commit 012e73faab8dc8617c6da4679715dae14f6cddd4
  Author: Daniel Stone <daniel@fooishbar.org>
  Date:   Fri Aug 15 18:25:53 2008 +0300

    Remove last remaining vestiges of Xprint support

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>