quota: Fix imapc backend not to try to find out mail's size.

This removes unnecessary FETCH RFC822.SIZE command sent to server when
expunging mails.

src/plugins/quota/quota-imapc.c

@@ -68,6 +68,7 @@ static int imapc_quota_init(struct quota_root *_root, const char *args,
 	}
 	if (root->box_name == NULL && root->root_name == NULL)
 		root->box_name = "INBOX";
+	_root->auto_updating = TRUE;
 	/* we'll never try to enforce the quota - it's just a lot of
 	   unnecessary remote GETQUOTA calls. */
 	_root->no_enforcing = TRUE;