tools: Use config.h from autoconf instead of "buildmakevars2header"

tools: Use config.h from autoconf instead of "buildmakevars2header"

This avoid the need to generate the _paths.h header when the
information is from autoconf anyway.

They are no more users of the "buildmakevars2header" macro, so it can
be removed from "Config.mk".

Also removed the extra "-f" flag where "$(RM)" is used (xl/Makefile).

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>