Revert "swarming: process 5000 bots at once for executor metrics"
Revert "swarming: process 5000 bots at once for executor metrics"

This reverts commit 68733ccfdc170207af73f1e6b2f0872864030824.

Reason for revert: https://crbug.com/1151408#c28

Original change's description:
> swarming: process 5000 bots at once for executor metrics
>
> This may mitigate the issue.
>
> _REQUEST_TIMEOUT_SEC is still used to prevent timeout error.
>
> Bug: 1151408
> Change-Id: I2510c5516c9d2bbe45b50ca59df383508464994c
> Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2691793
> Commit-Queue: Junji Watanabe <jwata@google.com>
> Reviewed-by: Junji Watanabe <jwata@google.com>
> Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>

Bug: 1151408
Change-Id: I7d06458c7be63b9ebbc06c0bf0b7cc0022c84292
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2717125
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Commit-Queue: Rubber Stamper <d516c4cc2192058ab8dae3d306acbdaf2ce6574f@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <d516c4cc2192058ab8dae3d306acbdaf2ce6574f@appspot.gserviceaccount.com>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py