vm_page: drop page_iter_lookup

[dougm]

Summary

The functions vm_page_iter_lookup and vm_page_iter_lookup_ge are just wrappers around vm_radix_iter_lookup and vm_radix_iter_lookup_ge, respectively. They server no real purpose, so drop them and use the vm_radix versions everywhere.

[kib]

You can make the functions static inline in a header to preserve the think layer of abstraction there but avoid the minor runtime overhead, if you want.