Move ValidRelations from Capturable to Captures

To better match weapon definitions

OpenRA.Mods.Common/Traits/Capturable.cs

@@ -22,9 +22,6 @@ namespace OpenRA.Mods.Common.Traits
 		[Desc("CaptureTypes (from the Captures trait) that are able to capture this.")]
 		public readonly BitSet<CaptureType> Types = default;
 
-		[Desc("What player relationships the target's owner needs to be captured by this actor.")]
-		public readonly PlayerRelationship ValidRelationships = PlayerRelationship.Neutral | PlayerRelationship.Enemy;
-
 		[Desc("Cancel the actor's current activity when getting captured.")]
 		public readonly bool CancelActivity = false;