Revert "[vm] Remove --causal-async-stacks flag"

This reverts commit b1f1aee94d8730d7d3b6def8a1fffec2181fcfb1.

Reason for revert: Some left-over uses in g3 need to removed first
(some were removed in b/380758599 but apparently there's some
usages left).

Original change's description:
> [vm] Remove --causal-async-stacks flag
>
> The flag isn't used anywhere in our tests or in embedder code. Turning
> it on will result in a VM startup error.
>
> We should therefore remove all uses of the flag and the flag itself.
>
> TEST=Existing test suite.
>
> Change-Id: I19dfba052df7948dfdb379c0610dab67ebbcd12d
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/204500
> Reviewed-by: Clement Skau <cskau@google.com>
> Commit-Queue: Martin Kustermann <kustermann@google.com>

TBR=kustermann@google.com,cskau@google.com

Change-Id: I03aad46f46153d5ea4ac2fcdd5685d0ef2a0d9af
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/204723
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>

https://dart.googlesource.com/sdk/+/0999d13ff3ceb5fdd83ea9935065f5c93906b253
diff --git a/commits.json b/commits.json
index c98f863..51e618c 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"99b752ed2c8f87bb1d13d89a7cee3fb9caa3b1f2",
   "external/github.com/flutter/flutter":"a76eb719dbacac4a91d36212c9b38480b5931197",
-  "sdk":"0740566438c510835b87cad99f088c7302c5ed5d"
+  "sdk":"0999d13ff3ceb5fdd83ea9935065f5c93906b253"
 }
\ No newline at end of file