platform/x86: intel_pmc_core: Remove unused EXPORTED API

Though ChromeOs uses the exported API as part of their S0ix failsafe
mechanism, there is no active consumer of this API in upstream kernel.

We can revisit this when ChromeOs kernel team is able to get their S0ix
failsafe framework in mainline.

Cc: Derek Basehore <dbasehore@chromium.org>
Cc: Rajat Jain <rajatja@google.com>
Link: https://patchwork.kernel.org/patch/9831229/

Suggested-by: Andriy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>