[X86] Remove model number based detection for 'pentiumpro', 'pentium2',...

[X86] Remove model number based detection for 'pentiumpro', 'pentium2', 'pentium3', 'pentium-m', and 'yonah' from getHostCPUName.

For model 6 CPUs, we have a fallback detection method based on
available features. That mechanism should be enough to detect
these early family 6 CPUs as they only differ in the features
used by the detection anyway.