outposts: replace migration with string backup handler

lifecycle/system_migrations/to_0_12.py

@@ -1,31 +0,0 @@
-from pickle import loads
-from typing import Any  # nosec
-
-from redis import Redis
-
-from lifecycle.migrate import BaseMigration
-from passbook.lib.config import CONFIG
-
-
-class Migration(BaseMigration):
-
-    def __init__(self, cur: Any, con: Any):
-        super().__init__(cur, con)
-        self.redis = Redis(
-            host=CONFIG.y("redis.host"),
-            port=6379,
-            db=CONFIG.y("redis.cache_db"),
-            password=CONFIG.y("redis.password"),
-        )
-
-    def needs_migration(self) -> bool:
-        keys = self.redis.keys(":1:outpost_*")
-        for key in keys:
-            value = loads(self.redis.get(key))  # nosec
-            if isinstance(value, str):
-                return True
-        return False
-
-    def run(self):
-        keys_to_delete = self.redis.keys(":1:outpost_*")
-        self.redis.delete(*keys_to_delete)

passbook/outposts/models.py

@@ -204,7 +204,11 @@ class OutpostState:
     def for_channel(outpost: Outpost, channel: str) -> "OutpostState":
         """Get state for a single channel"""
         key = f"{outpost.state_cache_prefix}_{channel}"
-        data = cache.get(key, {"uid": channel})
+        default_data = {"uid": channel}
+        data = cache.get(key, default_data)
+        if isinstance(data, str):
+            cache.delete(key)
+            data = default_data
         state = from_dict(OutpostState, data)
         state.uid = channel
         # pylint: disable=protected-access