staging: android: ion: Nuke ion_page_pool_init

ion_page_pool.c now is used to apply pool APIs for system heap, which do
not need do any initial at device_initcall. Therefore ion_page_pool_init
can be nuked.

Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>