client: remove unused code path using isolated for upload
client: remove unused code path using isolated for upload

https://crbug.com/1099655#c30

Bug: 1099655
Change-Id: Ia9147247b9d2ac15a12a82b960e58cfc9941d5df
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2886122
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

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