DOC: remove _agg_template_series

Co-authored-by: mroeschke <[email protected]>
Co-authored-by: rhshadrach <[email protected]>

Author: 3 people

scripts/validate_unwanted_patterns.py

@@ -29,7 +29,6 @@
     "_shared_docs",
     "_new_Index",
     "_new_PeriodIndex",
-    "_agg_template_series",
     "_agg_template_frame",
     "_pipe_template",
     "_apply_groupings_depr",