Remove Resource class and support functions.

tests/corelib/package_resource_test.dart

-// Copyright (c) 2015, 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.
-
-const sampleText = "Sample text file.";
-
-main() async {
-  const uriText = "package:package_test_data/resources/sample.txt";
-  const resource = const Resource(uriText);
-
-  if (resource.uri != Uri.parse(uriText)) {
-    throw "Incorrect URI: ${resource.uri}";
-  }
-
-  var text = await resource.readAsString();
-  if (!text.startsWith("Sample text file.")) {
-    throw "Incorrect reading of text file: $text";
-  }
-
-  var bytes = await resource.readAsBytes();
-  if (!compareBytes(bytes, sampleText.codeUnits)) {
-    throw "Incorrect reading of bytes: $bytes";
-  }
-
-  var streamBytes = [];
-  await for (var byteSlice in resource.openRead()) {
-    streamBytes.addAll(byteSlice);
-  }
-  if (!compareBytes(streamBytes, sampleText.codeUnits)) {
-    throw "Incorrect reading of bytes: $bytes";
-  }
-
-  if (!compareBytes(streamBytes, bytes)) {
-    throw "Inconsistent reading of bytes: $bytes / $streamBytes";
-  }
-}
-
-/// Checks that [bytes] starts with [expectedBytes].
-///
-/// The bytes may be longer (because the test file is a text file and its
-/// terminating line ending may be mangled on some platforms).
-bool compareBytes(bytes, expectedBytes) {
-  if (bytes.length < expectedBytes.length) return false;
-  for (int i = 0; i < expectedBytes.length; i++) {
-    if (bytes[i] != expectedBytes[i]) return false;
-  }
-  return true;
-}