build: spec: get rid of redundant defattr

References (first one provides some context):
https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/KEO7AX3JXR2TY6OVL4M7HDISZ6YIJNKU/#2UFET77NHMJTG4NA2ECRVH2KO3W56ZWD
https://github.com/rpm-software-management/rpm/commit/47ea5da7d
(~2004, rpm-4.4)

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>