Update Python lidar tutorials to use rasterio package

[bhass-neon]

Old RSDI lessons included long user-defined functions to read in the raster data. These lessons would be much simpler / cleaner using the Python packages rasterio. Also now we can download data tiles directly in Python instead of linking to obsolete Citrix Fileshare location.

Intro Lidar Lessons:

• [x] classify raster with thresholds - now https://www.neonscience.org/resources/learning-hub/tutorials/classify-chm-py
• [x] mask-rasters-py (https://www.neonscience.org/resources/learning-hub/tutorials/mask-rasters-py)
• [x] create-hillshade (https://www.neonscience.org/resources/learning-hub/tutorials/create-hillshade-py)
• [ ] merge-lidar-geotiff-py (https://www.neonscience.org/resources/learning-hub/tutorials/merge-lidar-geotiff-py)

Lidar Uncertainty:

• [ ] Exploring Uncertainty in LiDAR Data using Python (https://github.com/NEONScience/NEON-Data-Skills/tree/main/tutorials/Python/AOP/Lidar/uncertainty-and-validation/lidar_uncertainty_py)