x86: Remove invalid clwb test code

When X86_FEATURE_WAITPKG(CPUID.7.0:ECX.WAITPKG[bit 5]) supported,
".byte 0x66, 0x0f, 0xae, 0xf0" sequence no longer represents clwb
instruction with invalid operand but tpause instruction with %eax
as input register.

Execute tpause with invalid input triggers #GP with below customed
qemu command line:

qemu -kernel x86/memory.flat -overcommit cpu-pm=on ...

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Message-Id: <20211201092619.60298-1-zhenzhong.duan@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>