This reverts commit 720a8bab.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Make Mac SystemInfo reflect the currently active GPU on dual GPU machines
> 
> Currently, the GetSystemInfo() function (in gpu_info_util/SystemInfo_mac.mm)
> on dual GPU Macs always updates the active GPU field of the SystemInfo
> instance to the first non-Intel GPU it finds. This change overrides the
> activeGPUIndex field of the SystemInfo instance to reflect the current GPU
> instead of the non-intel GPU.
> 
> Bug: 985486, 984780, angleproject:3701
> Change-Id: Ia93f38f4a2f7728c05e99c83a940722bd3808766
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1752334
> Commit-Queue: Kenneth Russell <kbr@chromium.org>
> Reviewed-by: Zhenyao Mo <zmo@chromium.org>
> Reviewed-by: Kenneth Russell <kbr@chromium.org>

TBR=zmo@chromium.org,geofflang@chromium.org,kbr@chromium.org,dakshidnani@google.com

Change-Id: Iacf4b8433ac1aa4d30c51f08ddfc6489af440cc4
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 985486, 984780, angleproject:3701
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1757373Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>