Remove `keylen` from `LruCache`. (#9993)

`keylen` seems to be a thing that is frequently incorrectly set, and we don't really need it.

The only time it was used was to figure out if we had removed a subtree in `del_multi`, which we can do better by changing `TreeCache.pop` to return a different type (`TreeCacheNode`).

Commits should be independently reviewable.

1 files changed, 0 insertions, 1 deletions

diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py

index 3a4d027095..2ac24a2f25 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -270,7 +270,6 @@ class DeferredCacheDescriptor(_CacheDescriptorBase):
         cache = DeferredCache(
             name=self.orig.__name__,
             max_entries=self.max_entries,
-            keylen=self.num_args,
             tree=self.tree,
             iterable=self.iterable,
         )  # type: DeferredCache[CacheKey, Any]