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 JuliaLang/julia#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

sys/x86/x86/tsc.c

@@ -498,7 +498,7 @@ test_tsc(int adj_max_count)
  uint64_t *data, *tsc;
  u_int i, size, adj;
 
- if ((!smp_tsc && !tsc_is_invariant) || vm_guest)
+ if ((!smp_tsc && !tsc_is_invariant))
  return (-100);
  size = (mp_maxid + 1) * 3;
  data = malloc(sizeof(*data) * size * N, M_TEMP, M_WAITOK);