Remove waterwatch module (#228)

The WaterWatch web service was shut down and get_flood_stage() no longer
works. Remove waterwatch.py and its import from __init__.py.

Closes #137.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: thodson-usgs

dataretrieval/__init__.py

@@ -11,5 +11,4 @@
 from dataretrieval.streamstats import *
 from dataretrieval.utils import *
 from dataretrieval.waterdata import *
-from dataretrieval.waterwatch import *
 from dataretrieval.wqp import *