fix(atlas): remove unused imports in import_province_boundaries.py

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tooling/planet-gen/import_province_boundaries.py

@@ -53,8 +53,6 @@ import numpy as np
 import sqlite3
 
 from generate_atlas import (
-    GRID_W,
-    GRID_H,
     DB_PATH,
     ensure_atlas_schema,
     query_inhabited_bodies,
@@ -213,7 +211,6 @@ def _label_basins(fdir: np.ndarray, accum: np.ndarray) -> np.ndarray:
 
     # BFS flood: for each unlabeled cell, follow flow direction until a labeled
     # cell is reached; assign that label back along the path.
-    from collections import deque
 
     def _trace(r0: int, c0: int) -> int:
         path: list[tuple[int, int]] = []