This reverts commit 658ff200.

Reason for revert: Fails no-i18n bot: https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20-%20noi18n%20-%20debug/27826

Original change's description:
> [utils] Make BitField final
> 
> We have hundreds of classes that derive from {BitField} without adding
> any functionality. This CL switches all such occurrences to 'using'
> declarations instead.
> 
> Before:
>   class MyBitField : public BitField<int, 6, 4, MyEnum> {};
> After:
>   using MyBitField = BitField<int, 6, 4, MyEnum>;
> 
> This might reduce compilation time by reducing the number of existing
> classes.
> 
> The old pattern is forbidden now by making {BitField} final.
> 
> R=​yangguo@chromium.org
> 
> Bug: v8:9396, v8:7629
> Change-Id: I8a8364707e8eae0bb522af2459c160e3293eecbb
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1722565
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#62956}

TBR=yangguo@chromium.org,clemensh@chromium.org

Change-Id: I50234a09c77aa89fdcf1e01c2497cc08d3ac79a8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:9396, v8:7629
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1724377Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62958}