don't need to dispose room keys anymore, they are owned by the loader

src/matrix/DeviceMessageHandler.js

@@ -67,12 +67,4 @@ class SyncPreparation {
         this.newRoomKeys = newRoomKeys;
         this.newKeysByRoom = groupBy(newRoomKeys, r => r.roomId);
     }
-
-    dispose() {
-        if (this.newRoomKeys) {
-            for (const k of this.newRoomKeys) {
-                k.dispose();
-            }
-        }
-    }
 }

src/matrix/Sync.js

@@ -464,7 +464,6 @@ class SessionSyncProcessState {
 
     dispose() {
         this.lock?.release();
-        this.preparation?.dispose();
     }
 }