Revert "Dart2js testing: Add prefix files when running dart2js output on d8 or jsshell."

tools/testing/dart/runtime_configuration.dart

Index: tools/testing/dart/runtime_configuration.dart
diff --git a/tools/testing/dart/runtime_configuration.dart b/tools/testing/dart/runtime_configuration.dart
index 3fa2ef345a51f2606db18b7667bbbce4cba866e9..fd30dd9931b165908781672498d332ab5ec5a407 100644
--- a/tools/testing/dart/runtime_configuration.dart
+++ b/tools/testing/dart/runtime_configuration.dart
@@ -76,8 +76,6 @@ class RuntimeConfiguration {
     // TODO(ahe): Make this method abstract.
     throw "Unimplemented runtime '$runtimeType'";
   }
-
-  List<String> dart2jsPreambles(Uri preambleDir) => [];
 }
 
 /// The 'none' runtime configuration.
@@ -126,10 +124,6 @@ class D8RuntimeConfiguration extends CommandLineJavaScriptRuntime {
         commandBuilder.getJSCommandlineCommand(
             moniker, suite.d8FileName, arguments, environmentOverrides)];
   }
-
-  List<String> dart2jsPreambles(Uri preambleDir) {
-    return [preambleDir.resolve('d8.js').toFilePath()];
-  }
 }
 
 /// Firefox/SpiderMonkey-based development shell (jsshell).
@@ -148,10 +142,6 @@ class JsshellRuntimeConfiguration extends CommandLineJavaScriptRuntime {
         commandBuilder.getJSCommandlineCommand(
             moniker, suite.jsShellFileName, arguments, environmentOverrides)];
   }
-
-  List<String> dart2jsPreambles(Uri preambleDir) {
-    return ['-f', preambleDir.resolve('jsshell.js').toFilePath(), '-f'];
-  }
 }
 
 /// Common runtime configuration for runtimes based on the Dart VM.