Update devdoc: 5-adding-a-delete-button.md

[leemyongpakva]

What?

We don't use useEffect at last. We use SnackbarList of notices instead.

Why?

The code show that.

How?

So removing useEffect import and adding import SnackbarList, notices are needed.

Testing Instructions

No need to test. It's just coding logic.

Testing Instructions for Keyboard

Screenshots or screencast

Before	After

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