This reverts commit 313d4844.

Reason for revert: https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20gcc/6354

Original change's description:
> Reland^3 "[parser] Introduce UnoptimizedCompileFlags"
> 
> This is a reland of 0a59e0cb
> which was a reland of 146f5375
> which was a reland of d91679bf
> 
> Initializes the BackgroundCompileTasks's language_mode in the
> constructor (previously only initialized after successful parse) in case
> the parse failed. We still need to reset it after parse in case the
> language mode changed (because we encountered "use strict").
> 
> Original change's description:
> > [parser] Introduce UnoptimizedCompileFlags
> >
> > UnoptimizedCompileFlags defines the input flags shared between parse and
> > compile (currently parse-only). It is set initially with some values, and
> > is immutable after being passed to ParseInfo (ParseInfo still has getters
> > for the fields, but no setters).
> >
> > Since a few of the existing flags were output flags, ParseInfo now has a
> > new output_flags field, which will eventually migrate to a ParseOutputs
> > structure.
> >
> > Bug: v8:10314
> > Change-Id: If3890a5fad883bca80a97bf9dfe44d91797dc286
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2096580
> > Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> > Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> > Reviewed-by: Simon Zünd <szuend@chromium.org>
> > Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#66782}
> 
> TBR=ulan@chromium.org,szuend@chromium.org,rmcilroy@chromium.org
> 
> Bug: v8:10314
> Change-Id: Ieee0bbfade4fe0b56de03bff47a7364959608d6a
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2157367
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#67265}

TBR=leszeks@chromium.org

Change-Id: I90ac035caa76d4c4baf5ce207247d1ce5169fb2f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:10314
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2157370Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67266}