Meta server: remove unnecessary and potentially harmful permission check optimization with append allocations. One problem with is that the -EPERM returned by AllocateChunkForAppend() can potentially clash with -1 returned in other cases. The other problem is that the cached permissions in the record append cache can become stale / out of date. On the other hand this optimization has practically no benefit as it only affects the "permissions denied" case, and has no effect on the successful allocations.