Remove deprecated call Dart_Error from the API. There are no uses of it.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
===================================================================
--- runtime/vm/dart_api_impl.cc	(revision 28825)
+++ runtime/vm/dart_api_impl.cc	(working copy)
@@ -385,13 +385,6 @@
 }
 
 
-// Deprecated.
-// TODO(turnidge): Remove all uses and delete.
-DART_EXPORT Dart_Handle Dart_Error(const char* error) {
-  return Dart_NewApiError(error);
-}
-
-
 // TODO(turnidge): This clones Api::NewError.  I need to use va_copy to
 // fix this but not sure if it available on all of our builds.
 DART_EXPORT Dart_Handle Dart_NewApiError(const char* error) {