[server][auth] fix QueryRealms requires identity
[server][auth] fix QueryRealms requires identity

It's not used and the identity can be retrieved from s.User().

R=iannucci, vadimsh

Bug: 1343842
Change-Id: I23b474df4a22ce516d5297bbefb6e211274c2d13
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3778947
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Auto-Submit: Weiwei Lin <968518a24f41fef00b747498600e52b792d06ae0@google.com>
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go