[realms] Remove poolUser role from poolOwner.
[realms] Remove poolUser role from poolOwner.

In some security-sensitive pools it is important that NO ONE
other than preapproved service accounts can submit tasks. Such pools
are still "owned", but owners should not have implicit permission
to submit tasks. If this is actually desired, they should be
granted "poolUser" role explicitly.

R=aaef61ef98ffea505db831f310be2a0eb8492537@google.com

Change-Id: I608d105bb17b59a59f5eb4a105457ce609ee1935
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2415174
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

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