Skip FSM workloads which rely on nUpserted or nRemoved when Balancer is enabled

remove_multiple_documents.js (and possibly other FSM workloads) assume that the count returned to the client is correct. For multi-updates and multi-deletes, this is not the case if there is an active migration affecting the modified documents because those operations aren't versioned.

We should investigate which tests in the FSM suites are affected and figure out a strategy to make them robust to background migrations.