Log Message:
Clean up libXaw handling. [1/2]

- remove LIBXAW variable. It is handled by buildlink3.mk now
- simplify patches and Makefile in packages using libXaw
- in some cases force use of Xaw3d (won't build with Xaw)
- replace some directly included of x11/Xaw3d with mk/xaw.buildlink3.mk

In next part:
- replace more includes with mk/xaw.buildlink3.mk