[roll] Roll fuchsia [docs][zircon] Clarify that threads are not zx_task_kill-able

This contradicts the line below that explicitly says:
"Killing a thread is not supported" and the code shows that:
https://cs.opensource.google/fuchsia/fuchsia/+/master:zircon/kernel/lib/syscalls/task.cc;l=480

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/503593
Original-Revision: c551e276209473871e972bfb355c4a4608d31cd2
GitOrigin-RevId: b4033d3f5bed779e8f9ee7e2e3df7bfeab8fd639
Change-Id: I8545564af4af6fec1913c1d06793268f60f8aa73
diff --git a/stem b/stem
index 03c2d3c..b328648 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="5746a563703200a5ca100788e2a14d7eda9c28e4"/>
+             revision="c551e276209473871e972bfb355c4a4608d31cd2"/>
   </projects>
   <hooks>
     <hook name="install-environment"