[luci-py] revert error message at _get_memory_usage()
[luci-py] revert error message at _get_memory_usage()

Follow up for crrev.com/c/1980373/2/appengine/components/components/utils.py#b100

Change-Id: I303b9a304644f5515ce26b080ac657e786b1c71d
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1986596
Auto-Submit: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>

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