[resultdb] Fix -n flag
[resultdb] Fix -n flag

https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1931278
broke -n flag. Fix it.

Simplify the semantics too: from "up to N results of each type"
to simpler "up to N results".

R=1dcb292530f82960316cb3d87cd67c3f212b79cb@chromium.org

Change-Id: I5569d3ef71f0e5befd421d412c1f7f2580f5635e
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2186089
Commit-Queue: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Commit-Queue: Scott Lee <1dcb292530f82960316cb3d87cd67c3f212b79cb@chromium.org>
Auto-Submit: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Reviewed-by: Scott Lee <1dcb292530f82960316cb3d87cd67c3f212b79cb@chromium.org>

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