x86/time: drop vtsc_{kern, user}count debug counters

x86/time: drop vtsc_{kern, user}count debug counters

They either need to be transformed to atomics to work correctly
(currently they left unprotected for HVM domains) or dropped entirely
as taking a per-domain spinlock is too expensive for high-vCPU count
domains even for debug build given this lock is taken too often.

Choose the latter as they are not extremely important anyway.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>