KVM: selftests: Drop signal/kick from dirty ring testcase

KVM: selftests: Drop signal/kick from dirty ring testcase

Drop the signal/kick from dirty_log_test's dirty ring handling, as kicking
the vCPU adds marginal value, at the cost of adding significant complexity
to the test.

Asynchronously interrupting the vCPU isn't novel; unless the kernel is
fully tickless, the vCPU will be interrupted by IRQs for any decently
large interval.

And exiting to userspace mode in the middle of a sequence isn't novel
either, as the vCPU will do so every time the ring becomes full.

Link: https://lore.kernel.org/r/20250111003004.1235645-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>