[milo] exclude PendingBuildStates from API responses
[milo] exclude PendingBuildStates from API responses

No one uses PendingBuildStates in master JSON API responses.
Remove them, so we don't have to emulate them

Bug:
Change-Id: I2d6493076515b1709486268a451196f9c95c7f30
Reviewed-on: https://chromium-review.googlesource.com/719480
Commit-Queue: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Reviewed-by: Ryan Tseng <2190fe9a39b4920ec7bd59c848ec5cccd163056f@chromium.org>

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