x86: stop punishing VMs with low priority for TSC timecounter

I suspect that virtualization techniques improved from the time when we
have to effectively disable TSC use in VM. For instance, it was reported
(complained) in https://github.com/JuliaLang/julia/issues/38877 that
FreeBSD is groundlessly slow on AWS with some loads.

Remove the check and start watching for complaints.

Reviewed by: emaste, grehan
Discussed with: cperciva
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D27629