materialize-sql: don't CREATE TABLE IF NOT EXISTS, just do CREATE TABLE

Over time we have evolved SQL materializations to the point where they should never be trying to create a table that already exists.

Since they still do, this can sometimes lead to more difficult to debug errors in cases where a table exists but they materialization can't see it via the INFORMATION_SCHEMA queries.

It would be easier to troubleshoot permissions problems etc. if table creation queries failed if the table already exists.