[web] Fix channel deletion problem

Summary: Because of D8513, channel, subchannel, and thread deletion stopped working. This diff fixes this issue.

Test Plan: Run web app and check if channel, subchannel, and thread deletion are working.

Reviewers: ashoat, tomek

Reviewed By: ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8528

keyserver/src/deleters/thread-deleters.js

@@ -54,7 +54,7 @@ async function deleteThread(
   const threadIDs = await fetchContainedThreadIDs(threadID);
 
   const [{ threadInfos: serverThreadInfos }] = await Promise.all([
-    fetchServerThreadInfos({ threadIDs: new Set(threadID) }),
+    fetchServerThreadInfos({ threadIDs: new Set(threadIDs) }),
     rescindPushNotifs(
       SQL`n.thread IN (${threadIDs})`,
       SQL`IF(m.thread IN (${threadIDs}), NULL, m.thread)`,