Remove deprecated TextTheme members (#139255)

Part of: flutter/flutter#143956

Author: Renzo-Olivares

examples/api/lib/widgets/value_listenable_builder/value_listenable_builder.0.dart

@@ -88,7 +88,7 @@ class CountDisplay extends StatelessWidget {
       width: 100,
       height: 100,
       padding: const EdgeInsetsDirectional.all(10),
-      child: Text('$count', style: Theme.of(context).textTheme.headline4),
+      child: Text('$count', style: Theme.of(context).textTheme.headlineMedium),
     );
   }
 }

packages/flutter/lib/src/material/button_theme.dart

@@ -381,7 +381,7 @@ class ButtonThemeData with Diagnosticable {
   /// minimum size, internal padding, and shape.
   ///
   /// Despite the name, this property is not the [TextTheme] whose
-  /// [TextTheme.button] is used as the button text's [TextStyle].
+  /// [TextTheme.labelLarge] is used as the button text's [TextStyle].
   ButtonTextTheme getTextTheme(MaterialButton button) => button.textTheme ?? textTheme;
 
   /// The foreground color of the [button]'s text and icon when

packages/flutter/lib/src/material/popup_menu.dart

@@ -1507,7 +1507,7 @@ class _PopupMenuDefaultsM2 extends PopupMenuThemeData {
   late final TextTheme _textTheme = _theme.textTheme;
 
   @override
-  TextStyle? get textStyle => _textTheme.subtitle1;
+  TextStyle? get textStyle => _textTheme.titleMedium;
 
   static EdgeInsets menuHorizontalPadding = const EdgeInsets.symmetric(horizontal: 16.0);
 }