outputconfigurationstore: disable adaptive sync by default

I've seen too many driver bugs with VRR since we added it, ranging from displays blanking for a moment when enabling or disabling VRR to even turning off completely while it's actually used. There is also a secondary issue that many displays have some amount of brightness flicker while VRR is used, which we can't properly limit without new KMS APIs.

Some of these issues are rather bad, and while they're not our fault, it still gives people a bad user experience and bad impression of Plasma, so this should be turned off by default at least until the most severe issues are resolved.

This change does not affect existing configurations.