[roll] Roll fuchsia [starnix][vfs] Move file_system.rs up a level

This file was in its own subdirectory, but I don't see any reason for
that. Looks like it might have been some automated refactoring of the
codebase. This CL moves the file back to the normal place.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1270404
Original-Revision: 062a8b64e596bc69ddd2417a01876931d920e485
GitOrigin-RevId: cc3de155f33d738da24cb5b7e05793e178eeb665
Change-Id: Ie5a5f8a3040c0bd27e0d6b8dc06cbb22260183dd

stem

diff --git a/stem b/stem
index cc22c47..a56acf5 100644
--- a/stem
+++ b/stem
@@ -8,7 +8,7 @@
              root=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="03b456a26708c09f73aea0a9f6452192ddac5b1d"
+             revision="062a8b64e596bc69ddd2417a01876931d920e485"
              />
   </imports>
   <projects>