execute_test_sql() was an older test function that set up a test

database, set some model state, and then executed SQL, before tearing

down that database.
This wasn't as general as the name implied, and it was only called from

a single place. An upcoming change will be altering some of the test SQL

machinery, and in preparation, this function is being removed. Instead,

ensure_test_db() now allows for setting an end model state (part of

the former responsibility of execute_test_sql(), and the one call site

now just calls ensure_test_db() and execute_transaction().

Unit tests pass.