postgresql_query, postgresql_script: let psycopg2 do the list -> pg array conversion

[betanummeric]

fixes #411

This PR removes the logic which converts a query argument from a python list to a postgres array, because psycopg2 can do this better.

This changes the module arguments to SQL translation, so I'm not sure if this should be categorized as just a bugfix or a major change.

[Andersson007]

@betanummeric if it changes the existing user interface anyhow (like values, choices, return values, etc.) / can lead to playbooks that worked won't work anymore after upgrade to a version containing the proposed change - it'd be a major change

[betanummeric]

uhh, this PR is quite old already. But I think it is still justified.
The change size categorization mostly depends on whether we call the existing behavior a bug or a feature. It it like that for quite a while now, so it's probably a feature now -> major change. :/
I guess the PR is in draft only because it needs some testing.