rst: Collect procfs remaps at once

There's no need in separate call to prepare_procfs_remaps().
All remaps are collected one step earlier and we can do
open_remap_dead_process() right at once.

Also rename the latter routine.

✓ travis-ci: success for Sanitize initialization bits
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>