Revert "query/api: properly pass downsampling param (#1144)"

[bwplotka]

If I am not wrong downsampling on master is broken for 2days.

This reverts commit 7a767ef.

See: #1144 (comment)

Reason:

• It has to be in in milisecond but we already do that underneath in Querier: https://github.com/improbable-eng/thanos/blob/3b9afb435215e761ecd34b3ccfd69d9946f6f725/pkg/query/querier.go#L58
• Conversion does not make sense here as time.Duration is unit agnostic type, so we should do conversion in the moment of transformation to int64 only.

Tests are nice but they are assuming no-one converts resolution in further stack. Let's revert this and fix the getFor as it's done here: #1146

[brancz]

Just curious, wouldn't it make sense to rather remove the conversions lower in the stack?

[GiedriusS]

That's what I was talking about in the other PR. Because otherwise IMHO we would just be kicking the can further down the road until someone in the future again will get confused about what actual unit is being used. So I propose just using int64 and everywhere else consistently.

[bwplotka]

Still, can we revert first and then talk about improvements? (:

[GiedriusS]

Okay, so let's revert it and fix that interface in the new PR. Sorry for the inconvenience, I was completely oblivious to the querier code which divides this value once more