[roll] Roll fuchsia [reachability] Rehome to improve OWNERS semantics

This moves the `reachability` source into `//src/connectivity/policy` to
improve code ownership semantics.

Original-Bug: b/318379038
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/970055
Original-Revision: 83f4548dca362708bc8a484620c755aa15d300da
GitOrigin-RevId: ed9b34ddc3c771ceadce52f3ecd284d269d9c2a8
Change-Id: I54b54025b2ad41df75d39f20c25bcce861bcd7c8
diff --git a/stem b/stem
index 58a16a3..03a99d2 100644
--- a/stem
+++ b/stem
@@ -11,7 +11,7 @@
              githooks="integration/git-hooks"
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="e89a5425d4984b152fa7115adfcf2d6a98e9d625"/>
+             revision="83f4548dca362708bc8a484620c755aa15d300da"/>
   </projects>
   <hooks>
     <hook name="install-environment"