Remove deprecated sourceMapping syntax.

sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart

Index: sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart b/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
index 59f74d2a7b82bc83a12494221a225c791b2f4c82..93df11a7c8d708c1c862639d95b4a41b9204be64 100644
--- a/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
@@ -1670,18 +1670,10 @@ class CodeEmitterTask extends CompilerTask {
 
   String generateSourceMapTag(Uri sourceMapUri, Uri fileUri) {
     if (sourceMapUri != null && fileUri != null) {
-      // Using # is the new proposed standard. @ caused problems in Internet
-      // Explorer due to "Conditional Compilation Statements" in JScript,
-      // see:
-      // http://msdn.microsoft.com/en-us/library/7kx09ct1(v=vs.80).aspx
-      // About source maps, see:
-      // https://docs.google.com/a/google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit
-      // TODO(http://dartbug.com/11914): Remove @ line.
       String sourceMapFileName = relativize(fileUri, sourceMapUri, false);
       return '''
 
 //# sourceMappingURL=$sourceMapFileName
-//@ sourceMappingURL=$sourceMapFileName
 ''';
     }
     return '';