Revert "kvmclock: set scheduler clock stable"

This reverts commit ff7bbb9c

.
Sasha Levin is seeing odd jump in time values during boot of a KVM guest:

[...]
[    0.000000] tsc: Detected 2260.998 MHz processor
[3376355.247558] Calibrating delay loop (skipped) preset value..
[...]

and bisected them to this commit.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>