[web] Delete unused files in the engine (flutter#172035)

Delete unused files.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [ ] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [ ] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview
[Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
[test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md
[Features we expect every widget to implement]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement
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[breaking change policy]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes
[Discord]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md
[Data Driven Fixes]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

Author: harryterkelsen

engine/src/flutter/ci/licenses_golden/licenses_flutter

@@ -52663,7 +52663,6 @@ ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/path.dart + ../../.
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/path_metrics.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/picture.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/picture_recorder.dart + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/platform_message.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/raster_cache.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/rasterizer.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/render_canvas.dart + ../../../flutter/LICENSE
@@ -52719,7 +52718,6 @@ ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/pointer_converter.dart + ../.
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/profiler.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/raw_keyboard.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/renderer.dart + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/rrect_renderer.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/safe_browser_api.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/scene_builder.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/scene_painting.dart + ../../../flutter/LICENSE
@@ -55738,7 +55736,6 @@ FILE: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/path.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/path_metrics.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/picture.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/picture_recorder.dart
-FILE: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/platform_message.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/raster_cache.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/rasterizer.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/canvaskit/render_canvas.dart
@@ -55794,7 +55791,6 @@ FILE: ../../../flutter/lib/web_ui/lib/src/engine/pointer_converter.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/profiler.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/raw_keyboard.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/renderer.dart
-FILE: ../../../flutter/lib/web_ui/lib/src/engine/rrect_renderer.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/safe_browser_api.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/scene_builder.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/scene_painting.dart

engine/src/flutter/lib/web_ui/lib/src/engine.dart

@@ -100,7 +100,6 @@ export 'engine/pointer_converter.dart';
 export 'engine/profiler.dart';
 export 'engine/raw_keyboard.dart';
 export 'engine/renderer.dart';
-export 'engine/rrect_renderer.dart';
 export 'engine/safe_browser_api.dart';
 export 'engine/scene_builder.dart';
 export 'engine/scene_painting.dart';