Revert of Refactor SharedFunctionInfo::IsBuiltin. (patchset #1 id:1 of https://codereview.chromium.org/2505853003/ )

Reason for revert:
Breaks layout tests:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/11394

Original issue's description:
> Refactor SharedFunctionInfo::IsBuiltin.
>
> This method is a slight misnomer. What we actually want to know is
> whether the function was defined in a user-provided script.
>
> Also remove redundant Script::hide_source flag.
>
> R=bmeurer@chromium.org, ulan@chromium.org

TBR=bmeurer@chromium.org,ulan@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/2512463002
Cr-Commit-Position: refs/heads/master@{#41050}