This reverts commit fffcbaea.

Reason for revert: Breaks in Chromium (e.g. https://ci.chromium.org/p/v8/builders/ci/Linux%20V8%20FYI%20Release%20%28NVIDIA%29)

Original change's description:
> [counters] Fix reentrant timers for V8.Execute
>
> This CL fixes a long standing issue where reentering TimedHistograms
> scopes would cause spurious measurements. Only the non-nested scopes
> yielded correct results.
>
> Due to the changed numbers, the V8.Execute histogram is renamed to
> V8.ExecuteMicroSeconds. Note that this histogram is also guarded
> behind the --slow-histograms flag due to the additional overhead.
>
> Unlike before, it does no longer include time for external callbacks
> and only measures self time. The following example illustrates the
> new behaviour:
>
> 1. Enter V8:           |--+.......+--| self-time: 4 units (reported)
> 2. Exit V8 (callback):    |-+...+-|    self-time: 2 units (ignored)
> 3. Re-enter V8:             |---|      self-time: 3 units (reported)
>
> This would result in 2 histogram entries with 4 time units for the first
> V8 slice and 3 units for the nested part. Note that the callback time
> itself is ignored.
>
> This CL attempts to clean up how TimedHistograms work:
> - Histogram: the base class
> - TimedHistograms: used for time-related histograms that are not nested
> - NestedTimeHistograms: Extends TimedHistograms and is used for nested
>   histograms
>
> This CL changes Histograms to not measure time themselves. Measurements
> happen in the *HistogramScopes:
> - BaseTimedHistogramScope: Base functionality
> - TimedHistogramScope: For non-nested measurements
> - NestedTimedHistogramScope: For nested measurements
> - PauseNestedTimedHistogramScope: Ignore time during a given scope.
>   This is used to pause timers during callbacks.
>
> Additional changes:
> - ExternalCallbackScope now contains a PauseNestedTimedHistogramScope
>   and always sets VMState<EXTERNAL>
>
> Bug: v8:11946
> Change-Id: I45e4b7ff77b5948b605dd50539044cb26222fa21
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3001345
> Reviewed-by: Omer Katz <omerkatz@chromium.org>
> Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
> Reviewed-by: Victor Gomes <victorgomes@chromium.org>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Camillo Bruni <cbruni@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#76111}

Bug: v8:11946
Change-Id: I954de1afbabf101fb5d4f52eca0d3b80a723385b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3077153
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Owners-Override: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76138}