avm2: Fix incorrect method return values/types for some native methods

- `Vector$object`'s `push` and `shift` should return `*`, not `Object`
- `DisplayObjectContainer`'s `setChildIndex` returns `void`

Author: Lord-McSweeney

core/src/avm2/globals/VectorObject.as

@@ -170,7 +170,7 @@ package __AS3__.vec {
 
         AS3 native function map(callback:Function, receiver:Object = null):*;
 
-        AS3 native function pop():Object;
+        AS3 native function pop():*;
 
         AS3 native function push(... rest):uint;
 
@@ -179,7 +179,7 @@ package __AS3__.vec {
 
         AS3 native function reverse():Vector$object;
 
-        AS3 native function shift():Object;
+        AS3 native function shift():*;
 
         AS3 native function slice(start:Number = 0, end:Number = 2147483647):Vector$object;
 

core/src/avm2/globals/flash/display/display_object_container.rs

@@ -443,8 +443,6 @@ pub fn set_child_index<'gc>(
 
         validate_add_operation(activation, parent, child, target_index)?;
         add_child_to_displaylist(activation.context, parent, child, target_index);
-
-        return Ok(child.object2());
     }
 
     Ok(Value::Undefined)