Remove the crypto factories

pkg/crypto/lib/src/md5.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.
 
 part of crypto;
 
-// The MD5 hasher is used to compute an MD5 message digest.
-class _MD5 extends _HashBase implements MD5 {
-  _MD5() : super(16, 4, false) {
+/**
+ * MD5 hash function implementation.
+ *
+ * WARNING: MD5 has known collisions and should only be used when
+ * required for backwards compatibility.
+ */
+class MD5 extends _HashBase {
+  MD5() : super(16, 4, false) {
     _h[0] = 0x67452301;
     _h[1] = 0xefcdab89;
     _h[2] = 0x98badcfe;
     _h[3] = 0x10325476;
   }
 
   // Returns a new instance of this Hash.
   MD5 newInstance() {
     return new MD5();
   }
@@ skipping 53 matching lines @@
                             _r[i]));
       a = temp;
     }
 
     _h[0] = _add32(a, _h[0]);
     _h[1] = _add32(b, _h[1]);
     _h[2] = _add32(c, _h[2]);
     _h[3] = _add32(d, _h[3]);
   }
 }