Worker: Remove unnecessary error handling in WorkerOrWorkletScriptController::Initialize()

This is a follow-up for comments in the previous code review:
https://chromium-review.googlesource.com/c/chromium/src/+/1614645/6/third_party/blink/renderer/bindings/core/v8/worker_or_worklet_script_controller.cc#157

Error cases handled in WorkerOrWorkletScriptController::Initialize() never
happen according to the comments. This CL removes the cases.

Bug: n/a
Change-Id: I44ab6db7213cecb5cd6e31a66b70bb53b3829560
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1621791
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661659}
9 files changed