Get rid of support for string interpolation in #import strings.

tests/vm/dart/import_map_test.dart

-// Copyright (c) 2012, 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.
-//
-// VMOptions=--import_map=GOOGLE,. --import_map=SRC,mysrc --import_map=DART,.
-//
-// Dart test program for checking implementation of string
-// interapolation feature in import statements.
-
-#library('test1.dart');
-
-#import('${GOOGLE}/$SRC/test2.dart');
-#import('$SRC/test3.dart');
-
-int test1() {
-  return 1;
-}
-
-main() {
-  var result = test1() + test2() + test3();
-  Expect.equals(6, result);
-}