Revert "i386/cpu: Warn about why CPUID_EXT_PDCM is not available"

Revert "i386/cpu: Warn about why CPUID_EXT_PDCM is not available"

This reverts commit 00268e00027459abede448662f8794d78eb4b0a4.
(The only conflict is in the !is_tdx_vm() part of the condition,
which is safe to keep).

mark_unavailable_features() actively blocks usage of the feature,
so it is a functional change, not merely a emitting warning.
The commit was intended to merely warn if PDCM was enabled when
the performance counters are not, so revert it.

Reported-by: Christian A. Ehrhardt <christian.ehrhardt@canonical.com>
Analyzed-by: Daniel P. Berrangé <berrange@redhat.com>
Analyzed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250819150235.785559-1-pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>