deduplication: fix bug in auto-dedup when it is on page-server

No need to check opts.use_page_server, because in write_pagemap_loc
write is local anyway. it appeared that on page-server when saving
pages to images opts.use_page_server=true and no auto-dedup started,
so images were not null as expected.

Signed-off-by: Tikhomirov Pavel <snorcht@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>