`marl::Scheduler::setWorkerThreadCount()` and `marl::Scheduler::setThreadInitializer()` have been deprecated.
`marl::Scheduler::Config` is the new API.

This got missed from 45493.

See https://github.com/google/marl/issues/139 for context.

Bug: b/140546382
Change-Id: Ic09c196b4c81f316cbf73de5395757108c16945c