policies: rewrite cache_key to prevent wrong cache

# Conflicts:
#	passbook/core/signals.py
#	passbook/policies/engine.py
#	passbook/policies/process.py

passbook/core/signals.py

@@ -1,31 +1,7 @@
 """passbook core signals"""
-from django.core.cache import cache
 from django.core.signals import Signal
-from django.db.models.signals import post_save
-from django.dispatch import receiver
-from structlog import get_logger
-
-LOGGER = get_logger()
 
 user_signed_up = Signal(providing_args=["request", "user"])
 invitation_created = Signal(providing_args=["request", "invitation"])
 invitation_used = Signal(providing_args=["request", "invitation", "user"])
 password_changed = Signal(providing_args=["user", "password"])
-
-
-@receiver(post_save)
-# pylint: disable=unused-argument
-def invalidate_policy_cache(sender, instance, **_):
-    """Invalidate Policy cache when policy is updated"""
-    from passbook.policies.models import Policy, PolicyBinding
-    from passbook.policies.process import cache_key
-
-    if isinstance(instance, Policy):
-        LOGGER.debug("Invalidating policy cache", policy=instance)
-        total = 0
-        for binding in PolicyBinding.objects.filter(policy=instance):
-            prefix = cache_key(binding) + "*"
-            keys = cache.keys(prefix)
-            total += len(keys)
-            cache.delete_many(keys)
-        LOGGER.debug("Deleted keys", len=total)