Remove automated closing bracket comments in IntelliJ IDEA

And in the vs code editor, change this setting to false

"dart.closingLabels": true

You can find this setting easily. Go setting and search(Ctrl+f) dart.closingLabels

Update 24.11.2019:

If you want to customize the closing label color, you can do this. In vscode, open your settings.json file and set this setting

"workbench.colorCustomizations": {
    "dart.closingLabels": "#FF5733"

The checkbox is in Settings (Preferences) | Editor | General | Appearance, toggle 'Show closing labels in Dart source code'.