KVM: selftests: Always unlink memory regions when deleting (VM free)

KVM: selftests: Always unlink memory regions when deleting (VM free)

Unlink memory regions when freeing a VM, even though it's not strictly
necessary since all tracking structures are freed soon after.  The time
spent deleting entries is negligible, and not unlinking entries is
confusing, e.g. it's easy to overlook that the tree structures are
freed by the caller.

Link: https://lore.kernel.org/r/20240802201429.338412-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>