Replace st_concave_hull() (implemented with concaveman) with sf::st_concave_hull()

[elipousson]

Version version 1.0-11 of sf adds a new sf::st_concave_hull() function: https://r-spatial.github.io/sf/news/index.html#version-10-11

This introduces a name conflict for my own st_concave_hull(). I'm assuming that my own version is either superseded or should be rebuilt as a wrapper function around sf::st_concave_hull() so this issue is a placeholder to remind me to go back and look into it further.

[elipousson]

Fixed in May 1 commit.