x86/cpu: Remove Makefile rule for removed UMC CPU support

x86/cpu: Remove Makefile rule for removed UMC CPU support

Support for UMC CPUs was removed in

  7d328c5de43a ("x86/cpu: Remove CPU_SUP_UMC_32 support"),

but a Makefile rule for the support code remained. Remove it.

Fixes: 7d328c5de43a ("x86/cpu: Remove CPU_SUP_UMC_32 support")
Signed-off-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Ahmed S. Darwish <darwi@linutronix.de>
Link: https://patch.msgid.link/20260610033252.164571-1-enelsonmoore@gmail.com