Revert "Have compile_proto add _pb2.py files next to the .proto files."
Revert "Have compile_proto add _pb2.py files next to the .proto files."

This reverts commit 02643ea5db5d2c9667cea1a0dbe130674cdaa4c4.

Reason for revert: wrong solution for the bug

Original change's description:
> Have compile_proto add _pb2.py files next to the .proto files.
>
> Change-Id: I71c1ddeb2b29843dacc3e7bf37c03c598d37e03b
> Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/3193810
> Auto-Submit: Joanna Wang <bc6dfeb40460aa87d922e00661e02afbab58c45b@chromium.org>
> Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
> Commit-Queue: Joanna Wang <bc6dfeb40460aa87d922e00661e02afbab58c45b@chromium.org>

Change-Id: I364cbe19c82fba967a3c09ca3425ccdea7fa666b
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/3221879
Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Commit-Queue: Joanna Wang <bc6dfeb40460aa87d922e00661e02afbab58c45b@chromium.org>

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