fix(nwis): stop emitting a DeprecationWarning at import time

nwis.py warned at module top-level, and dataretrieval/__init__ star-imports
nwis, so `import dataretrieval` emitted a DeprecationWarning for every consumer
(including waterdata-only users) and failed to import entirely under
`-W error::DeprecationWarning`, which is common in CI.

Deprecation is already signaled where it matters: the @_deprecated decorator
emits a per-function warning on every nwis call. Removed the redundant
module-level warning; the per-function warnings are unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: thodson-usgs

dataretrieval/nwis.py

@@ -24,13 +24,12 @@
 except ImportError:
     gpd = None
 
-# Issue deprecation warning upon import
-warnings.warn(
-    "The 'nwis' services are deprecated and being decommissioned. "
-    "Please use the 'waterdata' module to access the new services.",
-    DeprecationWarning,
-    stacklevel=2,
-)
+# NOTE: deprecation is signaled per-function via the @_deprecated decorator
+# (see _warn_deprecated below), NOT at import time. A module-level
+# warnings.warn(DeprecationWarning) here fired on every `import dataretrieval`
+# (because dataretrieval/__init__ star-imports nwis), warning even
+# waterdata-only users and breaking any project that runs under
+# `-W error::DeprecationWarning`. The per-function warnings cover real usage.
 
 WATERDATA_BASE_URL = "https://nwis.waterdata.usgs.gov/"
 WATERDATA_URL = WATERDATA_BASE_URL + "nwis/"