Delete prebuilt/bar directory

This directory was used to test the cipd_to_git_roller.py recipe, which
is being deleted.

Bug: 352146834
Change-Id: I62edd4593b1237fe5f5ede48bf13698f9c426e56
Reviewed-on: https://fuchsia-review.googlesource.com/c/infra/roller-tests/integration/+/1078598
Commit-Queue: Oliver Newman <olivernewman@google.com>
Reviewed-by: Betram Lalusha <betramlalusha@google.com>
diff --git a/prebuilt/3/bar.txt b/prebuilt/3/bar.txt
deleted file mode 100644
index e69de29..0000000
--- a/prebuilt/3/bar.txt
+++ /dev/null