[schema2sql] Avoid "parsing" SQL statements for database initialization
A big SQL string was generated, then splitted. This caused bug if some value in
the schema (eg vocabulary, default) contained the separator (';').
To properly fix this, yield each individual statement instead of generating a
string.
Closes #14050899
[schema2sql] Drop most of the DB DROP related code
This code is dead for a while, it has been superseded by
`sql_drop_all_user_tables`.
Related to #14050899