qemu: Fix pit timer tick policy=delay

qemu: Fix pit timer tick policy=delay

By a mistake, for the VIR_DOMAIN_TIMER_TICKPOLICY_DELAY qemu
command line creation, 'discard' was used instead of 'delay'
in commit id '1569fa14'.

Test "kvm-pit-delay" is fixed accordingly to show the correct
option being generated.

Remove the (now) redundant kvm-pit-device tests. As it turns
out there is no need to specify both QEMU_CAPS_NO_KVM_PIT and
QEMU_CAPS_KVM_PIT_TICK_POLICY since they are mutually exclusive
and "kvm-pit-device" becomes just the same as "kvm-pit-delay".

Signed-off-by: Maxim Nestratov <mnestratov@virtuozzo.com>