x86/fpu: Remove PKRU handling from switch_fpu_finish()

PKRU is already updated and the xstate is not longer the proper source
of information.

 [ bp: Use cpu_feature_enabled() ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121456.708180184@linutronix.de