Drop ngwmn getters from _PUBLIC_GETTERS

tests/ngwmn_test.py is local-only work not yet in the repo. The ngwmn
module itself is committed, but no upstream tests reference it through
the conftest's selection path, so listing get_data/get_levels/get_sites
in _PUBLIC_GETTERS adds maintenance surface for no upstream benefit.
Add these back if/when ngwmn tests land.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: thodson-usgs

tests/conftest.py

@@ -81,10 +81,6 @@
         "get_record",
         "get_stats",
         "get_water_use",
-        # ngwmn
-        "get_data",
-        "get_levels",
-        "get_sites",
     }
 )