[roll] Roll fuchsia [build] Remove //build/unification

The last of the build unification scaffolding was removed over the last
~two weeks, and this is now just a hollow shell, or perhaps a monument
to days long gone.
There's still cleanups and IOUs in other pending changes. But I think
this is cause for celebration, so...

Original-Fixed: 60410
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/636522
Original-Revision: b8ac345f89f51b7b5af21a854f093729ed7d9dd3
GitOrigin-RevId: b0e15e47d7536951d0f288ab37de624d1c5126c7
Change-Id: I728dfb294b38bf79124ea8d0a2947cc9d133ac3e
diff --git a/stem b/stem
index 3c351b9..a43993c 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="b693458dec5f57311fd2ccaaefe2fa60e2dfa8e8"/>
+             revision="b8ac345f89f51b7b5af21a854f093729ed7d9dd3"/>
   </projects>
   <hooks>
     <hook name="install-environment"