Removing the drop shadow from a Scaffold AppBar in Flutter?

 To remove appbar drop down shadow set a AppBar constructor elevation: 0.0

The arguments primary, toolbarOpacity, bottomOpacity and automaticallyImplyLeading must not be null. Additionally, if elevation is specified, it must be non-negative.

If backgroundColor, elevation, shadowColor, brightness, iconTheme, actionsIconTheme, textTheme or centerTitle are null, then their AppBarTheme values will be used. If the corresponding AppBarTheme property is null, then the default specified in the property's documentation will be used.

appBar: AppBar(
   title: Text('App Title'),
   elevation: 0.0,
   bottomOpacity: 0.0,
),

To more : AppBar constructor