Drop Prometheus middleware from dramatiq settings (#234)

Prometheus client became optional in dramatiq:
https://github.com/Bogdanp/dramatiq/releases/tag/v2.0.0

Unfreeze dramatiq dependency

Author: amureki

pyproject.toml

@@ -44,7 +44,7 @@ test = [
   "redis",
 ]
 dramatiq = [
-  "dramatiq<2",
+  "dramatiq",
   "django-dramatiq",
 ]
 celery = [

tests/testapp/settings.py

@@ -151,7 +151,6 @@
 DRAMATIQ_BROKER = {
     "BROKER": os.getenv("DRAMATIQ_BROKER", "dramatiq.brokers.redis.RedisBroker"),
     "MIDDLEWARE": [
-        "dramatiq.middleware.Prometheus",
         "dramatiq.middleware.AgeLimit",
         "dramatiq.middleware.TimeLimit",
         "dramatiq.middleware.Callbacks",