Remove Defunct NWIS Functions

[thodson-usgs]

Recreate PR #216: Remove Defunct NWIS Functions

This PR resubmits the changes from PR #216 which removes four defunct NWIS legacy functions (get_gwlevels, get_discharge_measurements, get_pmcodes, and get_water_use) by replacing them with NameError exceptions that point users to the modernized waterdata equivalents.

The original PR #216 was superseded by linting changes (PR #219) on the main branch before being merged, which caused conflicts. This PR correctly recreates the exact logical changes from PR #216 directly on top of the newly linted main branch, ensuring we maintain ruff compliance while formally deprecating the defunct functions as planned.

All related tests and defunct data files have been removed, and the README has been updated to reflect the new API announcements identically to PR #216.

Notebook Modernization

In addition to the core API changes, a comprehensive review and modernization of 16 demo notebooks (including all legacy hydroshare examples) was performed:

• API Migration: Legacy nwis.get_dv(), nwis.get_iv(), and nwis.get_info() calls were upgraded to their modern waterdata equivalents.
• Defunct Removal: Defunct functions (get_water_use, get_pmcodes) were commented out or replaced with modern alternatives (get_reference_table) across all demos (e.g., R Python Vignette, WaterUse suite).
• Execution Validation: All notebooks were successfully re-executed using jupyter nbconvert in the local .venv environment to ensure they remain functional and generate correct plots with the new OGC long-format data schema.
• Clean State: Each notebook was processed with nb-clean to strip execution outputs and counts, ensuring a clean version-controlled state.

[ldecicco-USGS]

Looks good!