refactor(settings): drop SQL_ENGINE env variable as only postgres is supported

.env.example

@@ -9,7 +9,6 @@ SECRET_KEY=<GENERATE A SAFE SECRET KEY AND PLACE IT HERE>
 DJANGO_ALLOWED_HOSTS=localhost 127.0.0.1 [::1]
 OUTBOUND_PORT=9005
 
-SQL_ENGINE=django.db.backends.postgresql
 SQL_DATABASE=wygiwyh
 SQL_USER=wygiwyh
 SQL_PASSWORD=<INSERT A SAFE PASSWORD HERE>

app/WYGIWYH/settings.py

@@ -126,8 +126,8 @@ WSGI_APPLICATION = "WYGIWYH.wsgi.application"
 
 DATABASES = {
     "default": {
-        "ENGINE": os.environ.get("SQL_ENGINE", "django.db.backends.sqlite3"),
-        "NAME": os.environ.get("SQL_DATABASE", BASE_DIR / "db.sqlite3"),
+        "ENGINE": "django.db.backends.postgresql",
+        "NAME": os.environ.get("SQL_DATABASE"),
         "USER": os.environ.get("SQL_USER", "user"),
         "PASSWORD": os.environ.get("SQL_PASSWORD", "password"),
         "HOST": os.environ.get("SQL_HOST", "localhost"),