Do deletion updates after commit.

Do deletion updates after commit.

WikiPage::doDeleteArticleReal now triggers secondary data updates
(link tables, etc) only after the deletion proper is committed.
This is consistent with the way doEditContent applies secondary
data updates, and avoids nested transactions (e.g. by one of the
updates using a retry loop).

Change-Id: Ie4d96f77d210c9953104a0e6fb11ea8ed348c42a