Remove rdbms::Login::DBTYPE_IN_MEMORY

Atm we have a separate "type" for rdbms::Login::DBTYPE_IN_MEMORY. However, it behaves exactly the same as rdbms::Login::DBTYPE_IN_MEMORY. The main difference is that rdbms::Login::DBTYPE_IN_MEMORY has a pre-configured filename: "file::memory:?cache=shared". The other differences are rather small:

• stmtTest.cpp (can be merged with the sqlite case; I don't see why this is different)
• CatalogueFactoryFactory.cpp: we don't allow creating an SQLITE DB, but we do allow creating an in-memory DB...