Fix #415: Remove intl_utils related configuration that is no longer needed

Remove flutter_intl config block
Set flutter.generate to true to enable Flutter's built-in localization generation

Change-Id: I72293e166142946283dad6a40894e313c8587419

Author: calcitem

src/ui/flutter_app/pubspec.yaml

@@ -79,7 +79,7 @@ flutter_gen:
   output: lib/generated/assets/
 
 flutter:
-  generate: false
+  generate: true
   uses-material-design: true
   assets:
     - assets/files/git-branch.txt
@@ -148,9 +148,6 @@ flutter:
     - assets/databases/std_4_3_5_5.sec2
     - assets/databases/std_4_4_5_5.sec2
 
-flutter_intl:
-  enabled: true
-
 msix_config:
   display_name: Mill (N Men's Morris)
   publisher_display_name: Calcitem Studio