chore: remove error in console for example app

[josxha]

The PluginScaleBar page of the example app has the following exception in the console:

======== Exception caught by widgets library =======================================================
The following assertion was thrown while applying parent data.:
Incorrect use of ParentDataWidget.

The ParentDataWidget Flexible(flex: 1) wants to apply ParentData of type FlexParentData to a RenderObject, which has been set up to accept ParentData of incompatible type MultiChildLayoutParentData.

Usually, this means that the Flexible widget has the wrong ancestor RenderObjectWidget. Typically, Flexible widgets are placed directly inside Flex widgets.
The offending Flexible is currently placed inside a CustomMultiChildLayout widget.

The ownership chain for the RenderObject that received the incompatible parent data was:
  LayoutBuilder ← FlutterMap ← Flexible ← KeyedSubtree-[GlobalKey#1f663] ← _BodyBuilder ← MediaQuery ← LayoutId-[<_ScaffoldSlot.body>] ← CustomMultiChildLayout ← _ActionsScope ← Actions ← ⋯

This happens because FlutterMap is wrapped in a Flexible parent widget that is not needed.
By removing the wrapping Flexible the error gets removed.