Cleanup / Less defensive programming.

If these assumptions fail the build *should* fail.

.circleci/config.yml

@@ -600,8 +600,7 @@ jobs:
           name: "Install the built package"
           command: |
             # Work around CircleCI not supporting globbing in store_artifacts
-            mkdir -p /tmp/debian-13-package/dist
-            rm -f /tmp/debian-13-package/dist/tahoe-lafs_*.deb
+            mkdir /tmp/debian-13-package/dist
             mv /tmp/debian-13-package/tahoe-lafs_*.deb /tmp/debian-13-package/dist/
             dpkg -i /tmp/debian-13-package/dist/tahoe-lafs_*.deb
       - run: