[libc++] Remove <experimental/coroutine>

We've been shipping <coroutine> since LLVM 14, so LLVM 17 won't ship
the <experimental/coroutine> header per our policy for removing TSes.

Differential Revision: https://reviews.llvm.org/D108697

NOKEYCHECK=True
GitOrigin-RevId: 226c444b3882e085daf7c9f8e284cfad44838e32
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index 88a4859..268df3a 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -44,6 +44,10 @@
 Deprecations and Removals
 -------------------------
 
+- The ``<experimental/coroutine>`` header has been removed in this release. The ``<coroutine>`` header
+  has been shipping since LLVM 14, so the Coroutines TS implementation is being removed per our policy
+  for removing TSes.
+
 Upcoming Deprecations and Removals
 ----------------------------------