Drop support for SQLite databases

The production server uses PostgreSQL. No other databases are supported
and thus the support for SQLite is dropped. Consequently, the
migrate_sqlite2psql tool is also not needed anymore and is deleted.

Issue: HIC-192
Change-Id: I47f811c1d5ce81a8856b36ce9f6cf7b2be5da0f4
diff --git a/hiccup/settings.py b/hiccup/settings.py
index 9cdb991..fc3e2d1 100644
--- a/hiccup/settings.py
+++ b/hiccup/settings.py
@@ -103,8 +103,12 @@
 
 DATABASES = {
     "default": {
-        "ENGINE": "django.db.backends.sqlite3",
-        "NAME": os.path.join(BASE_DIR, "db.sqlite3"),
+        "ENGINE": "django.db.backends.postgresql_psycopg2",
+        "HOST": "",  # Connect to database through UNIX domain sockets
+        "PORT": "",  # Not needed for UNIX domain sockets
+        "NAME": os.environ.get("USER"),
+        "USER": os.environ.get("USER"),
+        "PASSWORD": "",  # Not needed for UNIX domain sockets
     }
 }