port database setup function to python

Hide the former PHP functions in a transition command until
they are removed.

nominatim/tools/exec_utils.py

@@ -2,13 +2,10 @@
 Helper functions for executing external programs.
 """
 import logging
-import os
 import subprocess
 import urllib.request as urlrequest
 from urllib.parse import urlencode
 
-from psycopg2.extensions import parse_dsn
-
 from ..version import NOMINATIM_VERSION
 from ..db.connection import get_pg_env