x86/cpuid: Remove obsolete CPUID(0x2) iteration macro

The CPUID(0x2) cache descriptors iterator at <cpuid/leaf_0x2_api.h>:

    for_each_leaf_0x2_desc()

has no more call sites.  Remove it.

Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250411070401.1358760-2-darwi@linutronix.de