selftests: kvm/x86: Fix the warning in pmu_event_filter_test.c

The following warning appears when executing
make -C tools/testing/selftests/kvm

x86_64/pmu_event_filter_test.c: In function 'vcpu_supports_intel_br_retired':
x86_64/pmu_event_filter_test.c:241:28: warning: variable 'cpuid' set but not used [-Wunused-but-set-variable]
  241 |         struct kvm_cpuid2 *cpuid;
      |                            ^~~~~
x86_64/pmu_event_filter_test.c: In function 'vcpu_supports_amd_zen_br_retired':
x86_64/pmu_event_filter_test.c:258:28: warning: variable 'cpuid' set but not used [-Wunused-but-set-variable]
  258 |         struct kvm_cpuid2 *cpuid;
      |                            ^~~~~

Just delete the unused variables to stay away from warnings.

Fixes: dc7e75b3b3ee ("selftests: kvm/x86: Add test for KVM_SET_PMU_EVENT_FILTER")
Signed-off-by: Jinrong Liang <cloudliang@tencent.com>
Message-Id: <20220119133910.56285-1-cloudliang@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>