AthenaPoolCnvSvc+OutputStreamAthenaPool: Update PHYSLITE branch split level to 1 (from 99)

As discussed in ATEAM-891, applying any branch split-level more than 1 breaks reading ElementLinks. At some point we switched to a global branch split-level of 99 in PHYSLITE upon request. Here we're going back from 99 to 1 to ensure we don't hit issues that are discussed in the ticket.

cc: @gemmeren @jcatmore @calpigia (please tag people that you think are relevant)