Moved two more Orders from RA to Common

Moved  Orders\EnterAlliedActorTargeter.cs  and  Orders\UnitOrderTargeter.cs  from OpenRA.Mods.RA to OpenRA.Mods.Common.
Also made a fix to an uncommon build issue regarding Common's reference to Eluant.dll. Not so much a problem as for consistency with the same reference in the other projects as they all reference it this way.
This is a bugfix - see the discussion in #6712.  This could do with being in its own commit that explains this, however.