Rename 'accessible' --> 'obj'

We moved from naming objects in the servers' object-trees `Accessible`s to
`ObjectRef`s. Variable names should be renamed aswell such to aim for least
confusion.

In this conversion I opt for the short 'obj' as variable name, it is short and
clear.

atspi-common/src/object_ref.rs

@@ -96,7 +96,7 @@ impl TryFrom<zvariant::OwnedValue> for ObjectRef {
 }
 
 impl From<ObjectRef> for zvariant::Structure<'_> {
-	fn from(accessible: ObjectRef) -> Self {
-		(accessible.name, accessible.path).into()
+	fn from(obj: ObjectRef) -> Self {
+		(obj.name, obj.path).into()
 	}
 }