x86/pci/ce4100: Remove unused 'struct sim_reg_op'

'struct sim_reg_op' wasn't ever used since it was introduced
14 years ago via:

  91d8037f

 ("ce4100: Add PCI register emulation for CE4100")

Remove it.

[ mingo: Improved the changelog. ]

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240507232348.46677-1-linux@treblig.org