This reverts commit b9191bd3.

Reason for revert: Clusterfuzz bugs
BUG=chromium:961507,chromium:961508

Original change's description:
> [class] implement private method declarations
>
> This patch implements the declarations of private methods, the access
> of private methods would be left to a future patch.
> When a private methods declaration is encountered, we now:
>
> - Create a brand symbol during class evaluation and store it in the
>   context.
> - Create the closures for the private methods
> - Load the brand from the context and store it in the instance in the
>   constructor.
>
> Design: https://docs.google.com/document/d/1T-Ql6HOIH2U_8YjWkwK2rTfywwb7b3Qe8d3jkz72KwA/edit#
>
> Bug: v8:8330
> Change-Id: I2d695cbdc8a7367ddc7620d627b318f779d36150
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1568708
> Commit-Queue: Joyee Cheung <joyee@igalia.com>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#61387}

TBR=rmcilroy@chromium.org,gsathya@chromium.org,verwaest@chromium.org,joyee@igalia.com

Change-Id: I429bbe8af9f94598de132814aa2c3ab9fa69b986
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:8330
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1605730
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61406}