Remove deprecated FlutterDriver.enableAccessibility (#143979)

https://github.com/flutter/flutter/issues/143956

packages/flutter_driver/lib/src/driver/driver.dart

@@ -179,15 +179,6 @@ abstract class FlutterDriver {
   /// Getter of webDriver.
   async_io.WebDriver get webDriver => throw UnimplementedError();
 
-  /// Enables accessibility feature.
-  @Deprecated(
-    'Call setSemantics(true) instead. '
-    'This feature was deprecated after v2.3.0-12.1.pre.'
-  )
-  Future<void> enableAccessibility() async {
-    await setSemantics(true);
-  }
-
   /// Sends [command] to the Flutter Driver extensions.
   /// This must be implemented by subclass.
   ///