message: Remove setFlushMode call
  [AB#658](https://dev.azure.com/fluidframework/internal/_workitems/edit/658)
  For more information about how to contribute to this repo, visit [this page](https://github.com/microsoft/FluidFramework/blob/main/CONTRIBUTING.md).
  ## Description
  Call to `setFlushMode` in unit tests was kept even after removal from interface for back-compat.
  `IContainerRuntimeBase.setFlushMode` is now fully removed.
diff: @@ -104,13 +104,6 @@ describeFullCompat("Flushing ops", (getTestObjectProvider) => {
  dataObject2map1 = await dataObject2.getSharedObject<SharedMap>(map1Id);
  dataObject2map2 = await dataObject2.getSharedObject<SharedMap>(map2Id);
  - // TODO: to remove these directives in https://dev.azure.com/fluidframework/internal/_workitems/edit/658
  - // @ts-expect-error older versions rely on the "setFlushMode" method
  - if (runtimeOptions?.flushMode !== undefined && dataObject1.context.containerRuntime.setFlushMode) {
  - // @ts-expect-error older versions rely on the "setFlushMode" method
  - dataObject1.context.containerRuntime.setFlushMode(runtimeOptions.flushMode);
  - }
  -
  await waitForCleanContainers(dataObject1, dataObject2);
  await provider.ensureSynchronized();
  }
  