x86/apb_timer: Drop unused TSC calibration

Drop the APB-timer TSC calibration, which hasn't been used since the
removal of Moorestown support by commit

  1a8359e4 ("x86/mid: Remove Intel Moorestown").

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200513100944.9171-1-johan@kernel.org