Update the README.md for the core/streams/ directory

Bug: 
Change-Id: Ifc41fef8f84a0703da21af3afeffed9e1c9d81e9
Reviewed-on: https://chromium-review.googlesource.com/571204Reviewed-by: Adam Rice <ricea@chromium.org>
Commit-Queue: Takeshi Yoshino <tyoshino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486698}

third_party/WebKit/Source/core/streams/README.md

-This directory contains the Blink implementation of the WHATWG Streams standard:
-https://streams.spec.whatwg.org/. There is also a legacy streams implementation.
+# core/streams/
 
-## V8 Extras ReadableStream Implementation
+This directory contains the Blink implementation of [the WHATWG Streams standard][1].
 
-- ByteLengthQueuingStrategy.js
-- CountQueuingStrategy.js
-- ReadableStream.js
-- ReadableStreamExperimentalPipeTo.js
-- ReadableStreamController.h
-- ReadableStreamOperations.{cpp,h}
-- UnderlyingSourceBase.{cpp,h,idl}
-- WritableStream.js
+We use [V8 extras][2] to implement it.
 
-These files implement ReadableStream using [V8 extras][1]. All new code should
-use this implementation.
-
-[1]: https://docs.google.com/document/d/1AT5-T0aHGp7Lt29vPWFr2-qG8r3l9CByyvKwEuA8Ec0
-
-## Old streams
-
-- Stream.{cpp,h,idl}
-
-These files support an old streams spec. They should eventually be removed, but
-right now XMLHttpRequest and Media Streams Extension code in Blink still
-depends on them.
+[1]: https://streams.spec.whatwg.org/
+[2]: https://docs.google.com/document/d/1AT5-T0aHGp7Lt29vPWFr2-qG8r3l9CByyvKwEuA8Ec0