Revert "kvmclock: Ensure proper env->tsc value for kvmclock_current_nsec calculation"

Revert "kvmclock: Ensure proper env->tsc value for kvmclock_current_nsec calculation"

This reverts commit 9b1786829aefb83f37a8f3135e3ea91c56001b56.

This patch fixed a hang introduced by commit a096b3a (kvmclock: Ensure
time in migration never goes backward, 2014-05-16), but it causes
a regression in migration whose cause is not quite clear.

Because of this, I'm choosing to revert both patches.  This trades a
2.1 regression for a bug that's been there forever.

Cc: agraf@suse.de
Cc: mtosatti@redhat.com
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>