[milo] remove unused cron job
[milo] remove unused cron job

/internal/cron/stats were removed in
https://chromium-review.googlesource.com/1839414

R=mwarton, nqmtuan

Bug: 1245505
Change-Id: I8ca98063e318c97b69ea89597a7d1285302be3e0
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3133491
Reviewed-by: Quang Minh Tuan Nguyen <7f5d2f4f6ce87649784e35ad551490ab8d89e8eb@google.com>
Commit-Queue: Quang Minh Tuan Nguyen <7f5d2f4f6ce87649784e35ad551490ab8d89e8eb@google.com>
Auto-Submit: Weiwei Lin <968518a24f41fef00b747498600e52b792d06ae0@google.com>

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