Remove InspectorNetworkAgent::replay_xhrs_to_be_deleted_

As XMLHttpRequest is now GarbageCollected, async destruction is
no longer needed.

Bug: 880027
Change-Id: Ieee63d77af98c4b053b567d477b5397b628448a2
Reviewed-on: https://chromium-review.googlesource.com/c/1383915
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634110}
2 files changed