mfd: pcf50633: Remove the header file core.h

mfd: pcf50633: Remove the header file core.h

The patches to remove all of the pieces of the pcf50633
have gone in and we're left with the header.

Remove it.

The pcf50633 was used as part of the OpenMoko devices but
the support for its main chip was recently removed in:
commit 61b7f8920b17 ("ARM: s3c: remove all s3c24xx support")

See https://lore.kernel.org/all/Z8z236h4B5A6Ki3D@gallifrey/

Signed-off-by: "Dr. David Alan Gilbert" <linux@treblig.org>
Link: https://lore.kernel.org/r/20250701145625.204048-1-linux@treblig.org
Signed-off-by: Lee Jones <lee@kernel.org>