[Extensions] Remove linked_ptr from web_request_api_unittest.cc

Remove a lingering linked_ptr usage.

Bug: 556939
Change-Id: I45840cfce318214aa4598dd5124c5cf134794d29
Reviewed-on: https://chromium-review.googlesource.com/c/1388927
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618669}
1 file changed