This reverts commit 8ae19e08.

Reason for revert:
Speculative revert for layout test:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/22215

See:
https://github.com/v8/v8/wiki/Blink-layout-tests

Original change's description:
> [esnext] re-implement template strings
> 
> - Add a new bytecode for the ToString operation, replacing the old
> intrinsic call (currently does not collect type feedback).
> - Add a new AST node to represent TemplateLiterals, and avoid
> generating unnecessary ToString operations in some simple cases.
> - Use a single feedback slot for each string addition, because the
> type feedback should always be the same for each addition
> 
> This seems to produce a very slight improvement on JSTests benchmarks
> and bench-ruben.js from v8:7415, and it's possible that type feedback
> for the ToString bytecode could provide more opportunities to eliminate
> the runtime call in TurboFan.
> 
> Doesn't touch tagged templates
> 
> BUG=v8:7415
> R=​rmcilroy@chromium.org, ishell@chromium.org, bmeurer@chromium.org
> 
> Change-Id: If5a8c68558431f058db894d65776324abf54218e
> Reviewed-on: https://chromium-review.googlesource.com/945408
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Commit-Queue: Caitlin Potter <caitp@igalia.com>
> Cr-Commit-Position: refs/heads/master@{#51853}

TBR=rmcilroy@chromium.org,caitp@igalia.com,ishell@chromium.org,bmeurer@chromium.org

Change-Id: Id0529b065493ffc20c8f2b1abacc4c1484c3c046
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7415
Reviewed-on: https://chromium-review.googlesource.com/958163Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51862}