Remove ScDocument* member from ScColumn
and re-use the one in ScAttrArray.

This saves 8 bytes and makes the code more
homogenious by using GetDoc() member everywhere.

(cherry picked from commit 1168a112)
Reviewed-on: https://gerrit.libreoffice.org/46680Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>
(cherry picked from commit dc3f0bde)

Change-Id: I16a94b7ef7c45ef3af14e812b45f255f39939a6e
Reviewed-on: https://gerrit.libreoffice.org/46990Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Ashod Nakashian <ashnakash@gmail.com>