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
Merge "Do deletion updates after commit."