FIX: https://github.com/flutter/samples/issues/1752 and https://githu… (#1753)

…b.com/flutter/samples/issues/1751

Fixes for:

The screen that shows Material elevation and row that says "Surface Tint
Color Only" has shadow and shown elevation dp is wrong.

FIX: https://github.com/flutter/samples/issues/1751
FIX: https://github.com/flutter/samples/issues/1752

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[CLA]: https://cla.developers.google.com/
[Discord]: https://github.com/flutter/flutter/wiki/Chat
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md

material_3_demo/lib/elevation_screen.dart

@@ -23,7 +23,10 @@ class ElevationScreen extends StatelessWidget {
               ),
             ),
           ),
-          ElevationGrid(surfaceTintColor: surfaceTint),
+          ElevationGrid(
+            surfaceTintColor: surfaceTint,
+            shadowColor: Colors.transparent,
+          ),
           SliverList(
             delegate: SliverChildListDelegate(<Widget>[
               const SizedBox(height: 10),
@@ -146,7 +149,7 @@ class _ElevationCardState extends State<ElevationCard> {
                 style: Theme.of(context).textTheme.labelMedium,
               ),
               Text(
-                '${widget.info.level.toInt()} dp',
+                '${widget.info.elevation.toInt()} dp',
                 style: Theme.of(context).textTheme.labelMedium,
               ),
               if (widget.surfaceTint != null)