feat: remove document.json from repo

frontend/app_flowy/packages/flowy_editor/example/pubspec.yaml

@@ -3,7 +3,7 @@ description: A new Flutter project.
 
 # The following line prevents the package from being accidentally published to
 # pub.dev using `flutter pub publish`. This is preferred for private packages.
-publish_to: 'none' # Remove this line if you wish to publish to pub.dev
+publish_to: "none" # Remove this line if you wish to publish to pub.dev
 
 # The following defines the version and build number for your application.
 # A version number is three numbers separated by dots, like 1.2.43
@@ -30,7 +30,6 @@ dependencies:
   flutter:
     sdk: flutter
 
-
   # The following adds the Cupertino Icons font to your application.
   # Use with the CupertinoIcons class for iOS style icons.
   cupertino_icons: ^1.0.2
@@ -58,15 +57,13 @@ dev_dependencies:
 
 # The following section is specific to Flutter packages.
 flutter:
-
   # The following line ensures that the Material Icons font is
   # included with your application, so that you can use the icons in
   # the material Icons class.
   uses-material-design: true
 
   # To add assets to your application, add an assets section, like this:
   assets:
-    - document.json
     - example.json
     - big_document.json
   #   - images/a_dot_ham.jpeg

frontend/app_flowy/packages/flowy_editor/pubspec.yaml

@@ -31,7 +31,6 @@ flutter:
     - assets/images/toolbar/
     - assets/images/popup_list/
     - assets/images/
-    - assets/document.json
   #   - images/a_dot_burr.jpeg
   #   - images/a_dot_ham.jpeg
   #