Default database probably shouldn't be set

Right now, there is default `edgedb` (or `main`, idk) databse when performing operations. I believe it's better not to set default database, as running any operation without specifing database directly can produce confusing query error / unwanted result. Users rarely need to do any operations on internal database.

No files or tests are named. Start by tracing how the CLI chooses a database when one is not supplied, then determine whether the internal database is selected by default. Done means operations without an explicit database no longer silently target that internal database and their resulting behavior is clear.

Written by the indexing model from the issue text.