Avoid pointless ifdef for iOS inside code not compiled for iOS anyway

The whole of svpbmp.cxx and svpvd.cxx are nowadays ifdeffed out for iOS.

Change-Id: Iac1f66457dc315ea86f86d12e1f6eb5bf4bcbb8c
Avoid a couple of pointless constant variables

Change-Id: If1dcb577d2dcc6477f43ad1be0e970e08d9093c6
ImageIO does not handle CGImageMasks

Change-Id: Ie5a35f68041a9c65658b9ce569ed3202c8a72ecb