intel_pstate: remove MSR test

x86_match_cpu will not match our cpuid unless APERF/MPERF flag is
set, so there is no need to do the manual check for this MSR.

Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>