Deprecate and remove web bundle directFromSellerSignals

The header-based version of directFromSellerSignals
(directFromSellerSignalsHeaderAdSlot) is unaffected.

Also, adds a WPT negative test, and uses a feature flag to control the
removal.

Usage metrics for web-bundle directFromSellerSignals are extremely low [0].

I2D&R thread [1].

[0] https://chromestatus.com/metrics/feature/timeline/popularity/5034

[1] https://groups.google.com/a/chromium.org/g/blink-dev/c/t9gHiTwV370

Bug: 384481095
Change-Id: I36d6ba9dbbeef4c434d00f5ba61cb1696bfbe11d

fledge/tentative/direct-from-seller-signals.https.window.js

@@ -503,6 +503,17 @@ subsetTest(promise_test, async test => {
   assert_true(dfss);
 }, 'Test directFromSellerSignals feature detection.');
 
+// The version of directFromSellerSignals based on web bundles preceded the
+// header-based version -- the web bundle version has been deprecated and
+// removed.
+subsetTest(promise_test, async test => {
+  let dfss = false;
+  navigator.runAdAuction({
+      get directFromSellerSignals() { dfss = true; }
+  }).catch((e) => {});
+  assert_false(dfss);
+}, 'Negative test for deprecated and removed web-bundle directFromSellerSignals.');
+
 subsetTest(promise_test, async test => {
   const uuid = generateUuid(test);
   await fetchDirectFromSellerSignals({ 'Buyer-Origin': window.location.origin });