Revert of [debugger] simplify fetching scripts for inspector. (patchset #6 id:100001 of https://codereview.chromium.org/2465833002/ )

Reason for revert:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/11118

Rule of thumb: As long as the tests have not migrated yet, you most certainly need a blink rebase whenever you change expectations.

Original issue's description:
> [debugger] simplify fetching scripts for inspector.
>
> The old code path is going to be removed with the debug context api.
>
> R=kozyatinskiy@chromium.org

TBR=kozyatinskiy@chromium.org,yangguo@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review-Url: https://codereview.chromium.org/2473273005
Cr-Commit-Position: refs/heads/master@{#40764}