Use QPageSize::name() for names of page sizes

Summary:
Drop the translations from KReportPageSizeInfo & pageSizeInfo, and use
what QPageSize::name() already provides.

Test Plan: Builds fine, shows the names from QPageSize as intended.

Reviewers: Kexi-Devel-list, staniek

Reviewed By: staniek

Subscribers: staniek

Tags: KReport

Differential Revision: https://phabricator.kde.org/D13713