Revert "Sharing of sources for corelib date implementation between VM and"

lib/compiler/implementation/lib/coreimpl_patch.dart

Index: lib/compiler/implementation/lib/coreimpl_patch.dart
diff --git a/lib/compiler/implementation/lib/coreimpl_patch.dart b/lib/compiler/implementation/lib/coreimpl_patch.dart
index 621cde9c6a794110b31654f706108d7ca8d25284..51de7cd3ea1fb423e6f1f5cf29b1b7a58d9a75e7 100644
--- a/lib/compiler/implementation/lib/coreimpl_patch.dart
+++ b/lib/compiler/implementation/lib/coreimpl_patch.dart
@@ -28,13 +28,6 @@ patch class DateImplementation {
     Primitives.lazyAsJsDate(this);
   }
 
-  patch static int _brokenDownDateToMillisecondsSinceEpoch(
-      int years, int month, int day, int hour, int minute, int second,
-      int millisecond, bool isUtc) {
-    return Primitives.valueFromDecomposedDate(
-        years, month, day, hour, minute, second, millisecond, isUtc);
-  }
-
   patch String get timeZoneName() {
     if (isUtc) return "UTC";
     return Primitives.getTimeZoneName(this);