Revert "Fix python bridge preventing logging transforms to root child (…

…#1097)" (#1098)

This reverts commit 891a5b2.

rerun_py/src/python_bridge.rs

@@ -443,8 +443,9 @@ fn log_transform(
     timeless: bool,
 ) -> PyResult<()> {
     let entity_path = parse_entity_path(entity_path)?;
-    if entity_path.is_root() {
-        return Err(PyTypeError::new_err("Transforms are between a child entity and its parent, so the root cannot have a transform"));
+    if entity_path.len() == 1 {
+        // Stop people from logging a transform to a root-entity, such as "world" (which doesn't have a parent).
+        return Err(PyTypeError::new_err("Transforms are between a child entity and its parent, so root entities cannot have transforms"));
     }
     let mut session = global_session();
     let time_point = time(timeless);