EventIndex: Remove an unused variable.

src/indexing/EventIndex.js

@@ -467,9 +467,6 @@ export default class EventIndex extends EventEmitter {
             // decryption keys, do we want to retry this checkpoint at a later
             // stage?
             const filteredEvents = matrixEvents.filter(this.isValidEvent);
-            const undecryptableEvents = matrixEvents.filter((ev) => {
-                return ev.isDecryptionFailure();
-            });
 
             // Collect the redaction events so we can delete the redacted events
             // from the index.