bbb-webrtc-sfu.service: do not set CPUSchedulingPolicy in a container

[davidmehren]

BBB 2.6 does not work correctly in LXC containers, as the unit file of bbb-webrtc-sfu sets CPUSchedulingPolicy, which is not supported there.

This adjusts the already existing override file to unset the option when bbb_container_compat is enabled

[defnull]

Not really a show-stopper for this RP, but we run BBB on privileged LXC containers that do support setting CPUSchedulingPolicy just fine, but still have to disable bbb_container_compat because installing auditd still fails on those. We then re-enable features disabled by bbb_container_compat=true in a later ansible task, and would also have to revert this change for the same reason.

So this is just a reminder for myself to do that when this gets merged ;)