[smoke-tests] Reverting concurrency back (#3501)
[smoke-tests] Reverting concurrency back (#3501)

### Description

I thought that concurrency control would be enough to avoid flakiness  with higher concurrency, but things are more flaky from the day I landed this. So reverting this to reduce flakiness back.

### Test Plan
CI

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