We noticed that almost every call site were loading both files,
the split isn't necessary anymore.

In some message tests, removed the absolute line number to allow future
changes.

Bug: v8:8726
Change-Id: I8527f0a1ecfa685aa01a5e2f5f47ddf1cb13a545
Reviewed-on: https://chromium-review.googlesource.com/c/1446452
Commit-Queue: Sven Sauleau <ssauleau@igalia.com>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59220}