Deprecate pgr_AlphaShape in 3.8

[robe2]

PostGIS has two ways of generating alphaShape.

If you have SFCGAL, which you can install using

CREATE EXTENSION postgis_sfcgal

You can use CG_AlphaShape (from PostGIS 3.5+) https://postgis.net/docs/CG_AlphaShape.html or by it's old name ST_AlphaShape for PostGIS 3.3+.

PostGIS has has ST_ConcaveHull for a while, even pre-3.0, but it was plpgsql based and slow and not always optimal for smallest encasing.
For PostGIS 3.3+ compiled with GEOS 3.10+ https://postgis.net/docs/ST_ConcaveHull.html is very fast and just as good as CGAL AlphaShape that both postgis_sfcgal and older pgRouting alphashape was based on.

As such there is no need for pgRouting to carry this function for newer versions of pgRoutng