Remove io and isolate from libraries for web sdk (#40259)

packages/flutter_tools/lib/src/build_runner/build_script.dart

diff --git a/packages/flutter_tools/lib/src/build_runner/build_script.dart b/packages/flutter_tools/lib/src/build_runner/build_script.dart
index cd3cfad..34d6c0c 100644
--- a/packages/flutter_tools/lib/src/build_runner/build_script.dart
+++ b/packages/flutter_tools/lib/src/build_runner/build_script.dart
@@ -78,8 +78,6 @@
   // Flutter web specific libraries.
   'ui',
   '_engine',
-  'io',
-  'isolate',
 ]);
 
 /// The builders required to compile a Flutter application to the web.