The schema lint tries to make sure we don't add or remove indices in
schema files (rather than as background updates), *unless* the table was
created in the same schema file.
The regex to pull out the `CREATE TABLE` SQL incorrectly didn't
recognise `IF NOT EXISTS`.
There is a test delta file that shows that we accept different types of
`CREATE TABLE` and `CREATE INDEX` statements, as well as an index
creation that doesn't have a matching create table (to show that we do
still catch it). The test delta should be removed before merge.
