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
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6096602
Reviewed-by: Mike Taylor <miketaylr@chromium.org>
Commit-Queue: Paul Jensen <pauljensen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1400484}

content/browser/interest_group/interest_group_browsertest.cc

@@ -751,6 +751,9 @@ class InterestGroupBrowserTest : public ContentBrowserTest {
          {blink::features::kFledgeAuctionDealSupport, {}},
          {blink::features::kFledgeDeprecatedRenderURLReplacements, {}},
          {blink::features::kFledgeSellerNonce, {}},
+         // TODO(crrev.com/c/6096602): Remove once implementation is removed.
+         {blink::features::kFledgeDirectFromSellerSignalsWebBundles, {}},
+         {blink::features::kFledgeSellerNonce, {}},
          {blink::features::kFledgeTrustedSignalsKVv2Support, {}}},
         /*disabled_features=*/
         {blink::features::kFencedFrames,