Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/PositionCallback.dartdoc

Index: lib/html/doc/interface/PositionCallback.dartdoc
diff --git a/lib/html/doc/interface/PositionCallback.dartdoc b/lib/html/doc/interface/PositionCallback.dartdoc
deleted file mode 100644
index 584fbac3d4dd20f1f2f3a8ed04be4fd8bc2e78fe..0000000000000000000000000000000000000000
--- a/lib/html/doc/interface/PositionCallback.dartdoc
+++ /dev/null
@@ -1,9 +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.
-
-// WARNING:
-//   This file contains documentation that is merged into the real source.
-//   Do not make code changes here.
-
-typedef bool PositionCallback(Geoposition position);