Removes dartc reliance on its own libraries, now can be targeted at any implementation's libraries

compiler/lib/implementation/string_base.dart

Index: compiler/lib/implementation/string_base.dart
diff --git a/compiler/lib/implementation/string_base.dart b/compiler/lib/implementation/string_base.dart
deleted file mode 100644
index f317d16a819b01b2b49fc2b7995c91f16d2776b3..0000000000000000000000000000000000000000
--- a/compiler/lib/implementation/string_base.dart
+++ /dev/null
@@ -1,23 +0,0 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-class StringBase {
-  static String createFromCharCodes(List<int> charCodes) native;
-
-  static String join(List<String> strings, String separator) {
-    String s = "";
-    for (int i = 0; i < strings.length; i++) {
-      if (i > 0) {
-        s = s.concat(separator);
-      }
-      s = s.concat(strings[i]);
-    }
-    return s;
-  }
-
-  static String concatAll(List<String> strings) {
-    return join(strings, "");
-  }
-
-}