This reverts commit 1e9808d3.

We shouldn't advertise libvirtd.socket activation, since currently
it means VM/network/... autostart won't work as expected.

We tried to find a middle ground by installing the config file without
an [Install] section, since systemd won't allow .socket to be enabled
without one... or at least it did do that; presently on f24 it allows
activating the socket quite happily. This also caused user confusion[1]

Just remove the socket file. I've filed a new RFE to track coming up
with a solution to the autostart problem[2], we can point users at that
if there's more confusion:

[1]: https://bugzilla.redhat.com/show_bug.cgi?id=1279348
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=1326136