Remove references to v1 embedding

[gmackall]

Fixes https://github.com/rafaelsetragni/awesome_notifications/issues/953.

We were not able to build the example app, because this plugin appears to require 3.19 due to changes in the TextTheme class - so this is a best effort removal, but not verified to build with flutter/engine#52022.

Searched for the removed classes with https://github.com/search?q=repo%3Arafaelsetragni%2Fawesome_notifications+%28%22io.flutter.view.FlutterMain%22+OR+%22io.flutter.view.FlutterNativeView%22+OR+%22io.flutter.view.FlutterView%22+OR+%22io.flutter.embedding.engine.plugins.shim%22+OR+%22io.flutter.app%22+OR+%22PluginRegistry.Registrar%22%29&type=code.

[rafaelsetragni]

Hi @gmackall,

Thank you so much for your contribution!

In fact, we need to remove these old v1 references from example app. However, please note that pull requests should be made to the development branch, not the master branch.

Our branching strategy is as follows:

• The master branch only contains versions that have been released to production.
• All new features and changes should be merged into the development branch first.
• Once the changes in the development branch are stable and tested, they are then grouped and merged into the release branch.
• Finally, the release branch is merged into the master branch.

Could you please update your pull request to target the development branch?

Thank you!

[gmackall]

Changed the branch!