KVM: selftests: Remove redundant setbuf()

Since setbuf(stdout, NULL) has been called in kvm_util.c with
__attribute((constructor)). Selftests no need to setup it in their own
code.

Signed-off-by: Shaoqin Huang <shahuang@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20230203061038.277655-1-shahuang@redhat.com


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>