KVM: selftests: Drop redundant vcpu_set_cpuid() from PMU selftest

Drop a redundant vcpu_set_cpuid() from the PMU test.  The vCPU's CPUID is
set to KVM's supported CPUID by vm_create_with_one_vcpu(), which was also
true back when the helper was named vm_create_default().

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-9-seanjc@google.com