[SYCL][DOC][Ordered Queue] Remove old proposal and make note of deprecation.

sycl/doc/extensions/OrderedQueue/OrderedQueue_v2.adoc

@@ -6,6 +6,8 @@ v0.2
 == Introduction
 This document presents an addition proposed for a future version of the SYCL Specification.  The goal of this proposal is to reduce the complexity and verbosity of using SYCL for programmers.
 
+NOTE: This proposal replaces the previous one that was based on a separate class for in-order queues.
+
 == Queue Order Properties
 Queues in SYCL are out-of-order by default.  SYCL constructs directed acyclic graphs to ensure tasks are properly ordered based on their data dependences.  However, many programs only require linear DAGs.  The overheads of constructing and managing DAGs are unnecessary for this class of program.  The `in_order` queue property is proposed to serve this class of programs by providing programmer-specified in-order semantics.  This property is used with the existing `property_list` mechanism that is part of the normal SYCL `queue`.