macOS: Delete unused FlutterRenderBackingStore (#168159)

All usages of this code were removed in
ed9d9bf372ba9ebd97446fb8a8f8b03f0f42986a during the great macOS renderer
refactor of 2022.

## 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 `///`).
- [X] 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.

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

<!-- Links -->
[Contributor Guide]:
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
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[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
https://dart.googlesource.com/external/github.com/flutter/flutter/+/e7d3223c619df00e2e851b83f97bcd3aba55f515
diff --git a/DEPS b/DEPS
index 6811085..deddf1c 100644
--- a/DEPS
+++ b/DEPS
@@ -236,7 +236,7 @@
 deps = {
   'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '695cf90eefb5c3b2e8ac83031534550532e3df42',
 
-  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '27006f6e958602d27185d9b04979f915a1cd9e4f',
+  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + 'e7d3223c619df00e2e851b83f97bcd3aba55f515',
 
   'flutter/engine/src/flutter/third_party/depot_tools':
   Var('chromium_git') + '/chromium/tools/depot_tools.git' + '@' + '580b4ff3f5cd0dcaa2eacda28cefe0f45320e8f7',
@@ -812,7 +812,7 @@
      'packages': [
        {
         'package': 'fuchsia/sdk/core/linux-amd64',
-        'version': 'uRZ63_whHk5Gt6MSMkuEAUwGxRR1Ue-ESkG6okXSvd0C'
+        'version': 'vqWDpBRU-9GJgmjRr0J5arGtwQu-ERs2WYtWU7_7VAIC'
        }
      ],
      'condition': 'download_fuchsia_deps and not download_fuchsia_sdk',
diff --git a/commits.json b/commits.json
index 5eba0ea..f85a3e9 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
-  "flutter":"27006f6e958602d27185d9b04979f915a1cd9e4f",
+  "flutter":"e7d3223c619df00e2e851b83f97bcd3aba55f515",
   "flutter/engine/src/flutter/third_party/dart":"695cf90eefb5c3b2e8ac83031534550532e3df42"
 }
\ No newline at end of file