Deprecate unused kernels

[hobu]

As discussed on the mailing list https://lists.osgeo.org/pipermail/pdal/2023-June/002709.html we seek to deprecate a number of kernels that are likely not seeing much use, especially given the expressiveness of the new Python bindings now available thanks to the @TileDB-Inc team.

We would deprecate the following kernels in 2.6.0, hide their documentation and prevent their default installation for 2.7.0, and complete their removal from the source and documentation tree at PDAL 2.8.0:

• chamfer
• delta
• density
• eval
• ground
• hausdorff
• random

For 2.6.0, we will add a DEPRECATED banner across the documentation page for each, and we will try to provide a Python or pdal pipeline example that demonstrates how to achieve what the kernel provided.

For 2.7.0, we will remove them from the default install

For 2.8.0, we will remove their implementation, documentation, and references in documentation.