[Coroutines][Docs] Remove frame packing as a TODO

This has already been done by @rjmccall in D76526 (49e5a97), and
9514c04. We should remove this from the docs.

Differential Revision: https://reviews.llvm.org/D90550

llvm/docs/Coroutines.rst

@@ -1535,10 +1535,6 @@ earlier passes.
 
 Areas Requiring Attention
 =========================
-#. A coroutine frame is bigger than it could be. Adding stack packing and stack 
-   coloring like optimization on the coroutine frame will result in tighter
-   coroutine frames.
-
 #. Take advantage of the lifetime intrinsics for the data that goes into the
    coroutine frame. Leave lifetime intrinsics as is for the data that stays in
    allocas.