Remove specs for postgresql 9.2 and 9.6 differences
We've deprecated PostgreSQL 9.2 and 9.6 long-time ago, but it seems we still have specs, testing differences from the two versions.
We should remove the ones for 9.2 and keep 9.6 calling it "current version" (remove any other specific test that only make sense in the context of 9.2 to 9.6 migration etc).