Delete unreachable default clause. (#8303)

The Dart analyzer will soon be changed so that if the `default` clause
of a `switch` statement is determined to be unreachable by the
exhaustiveness checker, a new warning of type
`unreachable_switch_default` will be issued. This parallels the
behavior of the existing `unreachable_switch_case` warning, which is
issued whenever a `case` clause of a `switch` statement is determined
to be unreachable. For details see
dart-lang/sdk#54575.

This PR deletes an unreachable `default` clause from `devtools` now,
to avoid a spurious warning when the analyzer change lands.

packages/devtools_app/lib/src/screens/inspector_v2/inspector_data_models.dart

@@ -269,7 +269,6 @@ class LayoutProperties {
           paddingB: parentSize.height - (size.height + parentData.offset.dy),
         );
       case SizeType.widths:
-      default:
         return (
           type: type,
           paddingA: parentData.offset.dx,