Remove dependence on Heighliner images

[DavidNix]

Right now, we assume Heighliner images which have sh and sleep. (Fyi, we use sleep for validator sentries because we wait before calling chaind start to give time for remote signer connection to be ready.)

Other containers, like Osmosis's canonical one, do not have these.

Therefore, the Operator only works with Heighliner-based images.

In the short-term, I think this is ok. We may need to add disclaimers saying as much.