Dont differentiate between ios_arm and ios_x64 in flutter_tools

All artifacts for iOS are universal.
diff --git a/packages/flutter_tools/lib/src/build_configuration.dart b/packages/flutter_tools/lib/src/build_configuration.dart
index 25c73a5..170c4bc 100644
--- a/packages/flutter_tools/lib/src/build_configuration.dart
+++ b/packages/flutter_tools/lib/src/build_configuration.dart
@@ -21,8 +21,7 @@
 
 enum TargetPlatform {
   android_arm,
-  ios_arm,
-  ios_x64,
+  ios,
   darwin_x64,
   linux_x64
 }