index: create function for deleting node from nodetree
A node is marked deleted by nt_insert(self, node, -1), but "-1" could
mean so many things (notably nullrev), so let's hide it in a
function. The function could possibly also remove nodes from the tree
in the future (it currently only marks them deleted).
Differential Revision: https://phab.mercurial-scm.org/D4004
#require docutils gettext
$ $TESTDIR/check-gendoc it
checking for parse errors