Remove the 'balancerRoundIntervalSetting' failpoint

The balancerRoundIntervalSetting failpoint is used as a means to control the balancer's sleep between cycles. With the balancer moving to the CSRS primary, setting this failpoint requires that the CSRS primary needs to be known at any time, which crates a problem with the stepdown suite.

Since it doesn't bring much value to the one test, which is using it we should remove it.