Revert "spec: Simplify setting features off by default"

Revert "spec: Simplify setting features off by default"

As it turns out, the rather complicated structure that is
currently used for enabling or disabling features in the libvirt
build does not cleanly map well to RPM's bcond feature.

Consequently, we need these back in order to support trivially
activating these features through extra macros as build inputs.

This reverts commit 31d687a3218c9072d7050dd608e013e063ca180f.

Signed-off-by: Neal Gompa <ngompa13@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>