Remove DefPersistentRooted and unneeded includes.
DefPersistentRooted is essentially a wrapper around unique_ptr and has no real reason to exist.
Part of SM52 migration, stage: SM45 compatible.
Patch by: Itms
Tested by: Freagarach
Refs #4893
Differential Revision: https://code.wildfiregames.com/D3086