Deleting custom block def in the workspace doesn't delete it in flyout

[bruh-9000]

Expected Behavior

Pressing backspace/delete on a custom block definer should remove the block from the flyout

Actual Behavior

Pressing backspace/delete on a custom block definer does not remove the block from the flyout

Steps to Reproduce

Explain what someone needs to do in order to see what's described in Actual behavior above

Steps to reproduce the behavior:

1. Create a custom block
2. Drag the custom block so it was selected
3. Press backspace/delete
4. Observe how the definition block disappears but in the flyout you can still use the block

System Details

All