Revert "AlertDialog widget scrollable by default (#49848)" (#51886)

This reverts commit 28f2c96a8a63ca75700b307692b3bc691d6d010c.
diff --git a/packages/flutter/lib/src/material/dialog.dart b/packages/flutter/lib/src/material/dialog.dart
index 4a68d13..be0f638 100644
--- a/packages/flutter/lib/src/material/dialog.dart
+++ b/packages/flutter/lib/src/material/dialog.dart
@@ -259,7 +259,7 @@
     this.insetPadding = _defaultInsetPadding,
     this.clipBehavior = Clip.none,
     this.shape,
-    this.scrollable = true,
+    this.scrollable = false,
   }) : assert(contentPadding != null),
        assert(clipBehavior != null),
        super(key: key);
diff --git a/packages/flutter/test/material/dialog_test.dart b/packages/flutter/test/material/dialog_test.dart
index 02e9293..2bd1161 100644
--- a/packages/flutter/test/material/dialog_test.dart
+++ b/packages/flutter/test/material/dialog_test.dart
@@ -1100,6 +1100,7 @@
           color: Colors.green,
           height: 1000,
         ),
+        scrollable: true,
       );
       await tester.pumpWidget(_buildAppWithDialog(dialog));
       await tester.tap(find.text('X'));
@@ -1119,6 +1120,7 @@
           color: Colors.orange,
           height: 1000,
         ),
+        scrollable: true,
       );
       await tester.pumpWidget(_buildAppWithDialog(dialog));
       await tester.tap(find.text('X'));
@@ -1144,6 +1146,7 @@
           color: Colors.orange,
           height: 400,
         ),
+        scrollable: true,
       );
       await tester.pumpWidget(_buildAppWithDialog(dialog));
       await tester.tap(find.text('X'));