Drop setuid from chrome-sandbox and keep Obsidian's tests in its package

Chromium sandboxes through unprivileged user namespaces on Arch-family
kernels, so the setuid-root helper is unnecessary. The watcher tests now run
from check() as checksummed package sources, leaving tests/ and the shared
Tests workflow untouched.

.github/workflows/test.yml

@@ -50,7 +50,6 @@ jobs:
               pacman -Syu --noconfirm git jq python libarchive
               python tests/oma-service-removal.py
               python tests/upstream-watch.py
-              python tests/obsidian-upstream.py
               ./bin/sync-upstream self-test
               ./bin/sync-rebuilds --self-test
               ./bin/omarchy-pkgs self-test