Don't expect operationTime to not change in causal_consistency_shell_support.js

Internal activity in the config server can lead to writes that advance operationTime, which can cause causal_consistency_shell_support.js to fail when it asserts that read commands don't advance operationTime. This check should be removed since there is no way to either prevent or ignore these writes.

This is the same base problem as SERVER-29111, but is triggered less frequently, only failing in suites with either more CSRS activity or that run more slowly (I've seen failues in sharding-auth and the continuous stepdown suite).