This reverts commit 9d34fa0c.

Reason for revert: Breaking test-parsing tests, see
https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Linux%20gcc%204.8/22942
https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Win64%20-%20msvc/5731

Original change's description:
> [parser] Optimize directive parsing especially for preparser
> 
> - Avoid allocating AstRawString in the preparser
> - Use fast LiteralEquals to compare the directive.
> 
> Bug: chromium:901250
> Change-Id: I178aca812f6c0ffa28d7f48b707316a5a99a2ac0
> Reviewed-on: https://chromium-review.googlesource.com/c/1314570
> Commit-Queue: Toon Verwaest <verwaest@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#57217}

TBR=ishell@chromium.org,verwaest@chromium.org

Change-Id: I47381358c5a8e9c39fe2af6e72481ebfe9d74a55
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:901250
Reviewed-on: https://chromium-review.googlesource.com/c/1314577Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57218}