Revert "Disable extra CPUs during Nanobench"

This reverts commit 32af335e7abbf562dad8f1bd21bb013610b8b021.

Reason for revert: many unhappy android bots

Original change's description:
> Disable extra CPUs during Nanobench
> 
> The previous experiment revealed that nanobench can
> run on any of the online CPUs, so rather than put
> the ones we don't need/want into powersave mode, just
> disable them.
> 
> Maybe in the future we can run CPU tests on the big
> or LITTLE cpus to get perf data on higher end or
> lower end cpus, but only if we get very stable
> results from this.
> 
> Bug: skia:7378
> notry=true
> notreechecks=true
> Change-Id: I057513a691093e7f73c0f5790e17fab1a5ec0bc4
> Reviewed-on: https://skia-review.googlesource.com/84820
> Reviewed-by: Kevin Lubick <kjlubick@google.com>
> Commit-Queue: Kevin Lubick <kjlubick@google.com>

TBR=borenet@google.com,mtklein@google.com,kjlubick@google.com

Change-Id: I23c37a6bde631e95f0b4ae7277ec8fcf325a00e9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:7378
Reviewed-on: https://skia-review.googlesource.com/84921
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
22 files changed