Remove comment-start-skip preset in tree-sitter indentation engine

Remove comment-start-skip preset in tree-sitter indentation engine

Comment indentation should use a adaptive-fill-based indent, rather
than comment-start-skip.

Also remove manual description of removed variables in treesit.el and
add documentation for n-p-gp upon request.

* doc/lispref/modes.texi (Parser-based Indentation)
* lisp/treesit.el (treesit-simple-indent-presets): Add n-p-gp, remove
treesit-comment-start/end, remove comment-start-skip.

* doc/lispref/parsing.texi (Tree-sitter major modes): Remove
treesit-comment-start/end.