This reverts commit e084eea6.

Reason for revert:
https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20UBSanVptr/builds/3163

Original change's description:
> Fix SourcePositionInfo for wasm
> 
> In wasm we often don't have a SharedFunctionInfo associated with a
> compilation job, so we can't get a Script. Just print "unknown" in
> these cases (instead of crashing).
> 
> R=​titzer@chromium.org
> CC=​​herhut@chromium.org
> 
> Bug: chromium:840757, v8:7738
> Change-Id: I850c6adfd9e07c9a0f6dd018f1a9314feb89d887
> Reviewed-on: https://chromium-review.googlesource.com/1049632
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Reviewed-by: Ben Titzer <titzer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#53080}

TBR=titzer@chromium.org,clemensh@chromium.org

Change-Id: Ib2020ea3f2b778df9fe50ccbe803938f2f4fd709
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:840757, v8:7738
Reviewed-on: https://chromium-review.googlesource.com/1051265Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53082}