[roll] Roll fuchsia [sestarnix] Remove create_unlabeled_file() and update tests

Remove the create_unlabeled_file() helper, leaving tests that
specifically need label-less files to arrange that themselves. This
is intended to avoid the problem of tests mis-using the
create_unlabeled_file() helper where create_file() would work.

Tests are also migrated to "use testing" and to refer to the test-
helpers via the "testing::" prefix, for clarity.

Original-Bug: 351195217
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1151275
Original-Revision: 50287008202b66826047aa142ca113f4fbd0defd
GitOrigin-RevId: 30cf448db7292786f001fb3de5a6b90214b6ae01
Change-Id: I7b517242cea3394dd27449bf1a4d6a487b4ba1eb

Author: Wez

stem

@@ -11,7 +11,7 @@
              githooks="integration/git-hooks"
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="1faf07f1ed89a67ad92f9f5c130b41d4e57c2052"/>
+             revision="50287008202b66826047aa142ca113f4fbd0defd"/>
   </projects>
   <hooks>
     <hook name="install-environment"