Don't save and restore the interwiki table
In fact it always has zero rows. Well, at least it does until
ApiQuerySiteinfoTest::testInterwikiMap() inserts two rows without using
@group Database, and then it has two rows from then on. It's meant to
have zero rows.
This saves time and memory.
Revert of f17feae3a991de9f54e0f57d91fe95bf84211fcb