Remove workaround for compiler dill-initialization. (#20541)

Workaround is not needed since real fix has landed in dart sdk: https://dart-review.googlesource.com/c/sdk/+/62729.

packages/flutter_tools/lib/src/compile.dart

@@ -341,7 +341,6 @@ class ResidentCompiler {
       '--incremental',
       '--strong',
       '--target=flutter',
-      '--initialize-from-dill=foo' // TODO(aam): remove once dartbug.com/33087 fixed
     ];
     if (outputPath != null) {
       command.addAll(<String>['--output-dill', outputPath]);