This reverts commit 748de1e5.

Reason for revert: Fails compilation (unused variable): https://ci.chromium.org/p/v8/builders/ci/V8%20Fuchsia/10879

Original change's description:
> [fuchsia] Replace zx_clock_get() with zx_clock_get_new().
> 
> zx_clock_get() signature is being replaced to report errors.
> As part of a soft transition, zx_clock_get_new() is introduced with
> the final function signature.
> 
> Bug: chromium:963956
> Change-Id: Ia6d0f4fc560bd9149683011099b064540b54edd6
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1616545
> Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
> Reviewed-by: Wez <wez@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#61591}

TBR=wez@chromium.org,fdegans@chromium.org

Change-Id: I14a97f6510f6fbd6b3698a3549def8feb128f0ff
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:963956
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1617241Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61593}