vfs: Remove irixacl module (all the fucntions in it are unimplemented)
Put prototypes of modules/vfs_irixacl.c to new modules/vfs_irixacl.h. Thereby (hopefully) fixing the potential build problems with IRIX acls. Michael (This used to be commit 61c201d416bbc37950b980e8598b7ef1292336bc)