WhatsApp Block: issues when removing child button block

### Quick summary

The WhatsApp button block creates a `send message` block with a `WhatsApp button` block nested within it.

When a user tries to delete the block it reappears on reload of editor. Because of the UI of gutenberg, users typically end up deleting the Button block and not the parent send message block that remains invisible. The whatsapp button gets added again

### Steps to reproduce

1. Create a new page or post
2. Add WhatsApp block and save changes.
3. Reload browser, and click and delete the whatsapp button. It removes the button. Save changes. There is no indication of the parent `Send a message` block being still active.
4. Reload the browser, the button reappears.

Uploading whatsapp-bug.mov…

### What you expected to happen

Ideal case - The parent Send a message block should get deleted when someone deletes the whatsapp button.

Next-to-ideal : Show a dummy block in editor that the `Send message` block is still present.

### What actually happened

Described in the video and details above.

### Context

36020401-hc

### Simple, Atomic or both?

Simple, Atomic

### Theme-specific issue?

_No response_

### Browser, operating system and other notes

MacOS - Vivaldi 5.3.2679.68

( happens across different browsers though )

### Reproducibility

Consistent

### Severity

Some (< 50%)

### Available workarounds?

Yes, difficult to implement

### Workaround details

Use the list view and delete the parent `Send a message` block

Start by reproducing the issue in the Gutenberg editor with the WhatsApp block, then inspect how the nested Send a message and WhatsApp button blocks are removed. Done means deleting the child also removes the parent, or leaves a visible parent block that can be deleted, with the button staying absent after reload.

Written by the indexing model from the issue text.