libtevent: rework dependencies for deterministic build

Since waf configure infrastructure is a body blow compared to reasonable
autoconf script from packager point of view, samba support libs need
feature-disable-patches. This one is for libtevent removing libcap
(introduced by libldap_r) and attr.

Signed-off-by: Jens Rehsack <sno@netbsd.org>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>