[cluster-test] Remove experiment_interval
[cluster-test] Remove experiment_interval

I don't even remember why we have it, but looks like we were sleeping for 15 seconds between each experiment.

Most likely it was because we did not fully recovery between experiments and our health checks did not catch it.

I think now health checks should be in a good shape, so we do not need this.

As we are going to have more and more experiments in nightly, we don't really want to waste additional 15 seconds on each experiment

Closes: #4723
Approved by: snakech

libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core