Clear expiration flag after user operation removed?

[wanliqun]

After we removed the expired user operation, we might need to clear the expiration datetime for it like delete(e.seenAt, userOpHash). This is because if the bundle transaction is successfully mined to block but reverted due to some reason, user tends to send the user operation again to the mempool, and will never be included to next bundle transaction due to expiration drop.

// DropExpired returns a BatchHandlerFunc that will drop UserOperations from the mempool if it has been around
// for longer than the TTL duration.
func (e *ExpireHandler) DropExpired() modules.BatchHandlerFunc {
	return func(ctx *modules.BatchHandlerCtx) error {
		end := len(ctx.Batch) - 1
		for i := end; i >= 0; i-- {
			hash := ctx.Batch[i].GetUserOpHash(ctx.EntryPoint, ctx.ChainID)
			if seenAt, ok := e.seenAt[hash]; !ok {
				e.seenAt[hash] = time.Now()
			} else if seenAt.Add(e.ttl).Before(time.Now()) {
				ctx.MarkOpIndexForRemoval(i)
			}
		}
		return nil
	}
}