Remove legacy restart code

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index 918e3ccc25df2cb34fda3c86754083e822bb3e47..4a034a24ca76235bc57b87c2ed89d69a3ef0df61 100644
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -132,10 +132,7 @@ typedef struct _Dart_Isolate* Dart_Isolate;
  *   occur in any function which triggers the execution of Dart code.
  *
  * - Fatal error handles are produced when the system wants to shut
- *   down the current isolate. Sometimes a fatal error may be a
- *   restart request (see Dart_IsRestartRequest). If the embedder does
- *   not support restarting the VM, then this should be treated as a
- *   normal fatal error.
+ *   down the current isolate.
  *
  * --- Propagating errors ---
  *
@@ -312,17 +309,6 @@ DART_EXPORT bool Dart_IsCompilationError(Dart_Handle handle);
 DART_EXPORT bool Dart_IsFatalError(Dart_Handle handle);
 
 /**
- * Is this error a request to restart the VM?
- *
- * If an embedder chooses to support restarting the VM from tools
- * (such as a debugger), then this function is used to distinguish
- * restart requests from other fatal errors.
- *
- * Requires there to be a current isolate.
- */
-DART_EXPORT bool Dart_IsVMRestartRequest(Dart_Handle handle);
-
-/**
  * Gets the error message from an error handle.
  *
  * Requires there to be a current isolate.