This reverts commit 77b24c06.

Reason for revert: Broke M83 feature freeze. Reland after the M83 branch cut.

Original change's description:
> [class] Ship private methods and accessors
> 
> Turns --harmony-private-methods on by default.
> 
> Intent to ship: https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/HLpO-HC8aKc/TT32fUNPBAAJ
> ChromeStatus page: https://www.chromestatus.com/feature/5700509656678400
> 
> Bug: v8:8330
> Change-Id: I0d9b21cddd5418be8e7059c24fa05ab98de667b9
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2110890
> Reviewed-by: Shu-yu Guo <syg@chromium.org>
> Commit-Queue: Joyee Cheung <joyee@igalia.com>
> Cr-Commit-Position: refs/heads/master@{#66933}

TBR=syg@chromium.org

Change-Id: Idbcb09fadd4779e5c2ee9b1ae52b7fba5bcb236e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:8330
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2130450Reviewed-by: Joyee Cheung <joyee@igalia.com>
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Cr-Commit-Position: refs/heads/master@{#66934}