There a few things we could cleanup:

__hs_start_internal_session is a one line wrapper, only used once, we could get rid of it.
Same for __hs_release_internal_session
Same for __wt_hs_close and this one has the description is "Destroy the database's history store." while it only does F_CLR(S2C(session), WT_CONN_HS_OPEN).