Removing label part assertions that no longer apply (#676)

## Summary

The job does not support multi-window and multiple labels

## Checklist
- [ ] Added Unit Tests
- [ ] Covered by existing CI
- [ ] Integration tested
- [ ] Documentation update



<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Refactor**
- Removed internal validation checks related to label join parts and
aggregations, simplifying the label parts handling process. No changes
to the user interface or exported functions.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: ezvz <[email protected]>

Author: varant-zlai

api/python/ai/chronon/join.py

@@ -281,24 +281,6 @@ def LabelParts(
     )
     label_metadata = api.MetaData(executionInfo=exec_info)
 
-    for label in labels:
-        if label.groupBy.aggregations is not None:
-            assert len(labels) == 1, "Multiple label joinPart is not supported yet"
-            valid_agg = (
-                len(label.groupBy.aggregations) == 1
-                and label.groupBy.aggregations[0].windows is not None
-                and len(label.groupBy.aggregations[0].windows) == 1
-            )
-            assert valid_agg, (
-                "Too many aggregations or invalid windows found. "
-                "Single aggregation with one window allowed."
-            )
-            valid_time_unit = (
-                label.groupBy.aggregations[0].windows[0].timeUnit
-                == common.TimeUnit.DAYS
-            )
-            assert valid_time_unit, "Label aggregation window unit must be DAYS"
-
     return api.LabelParts(
         labels=labels,
         metaData=label_metadata,