Simplify [Dune_project.default_name] (#2904)
Simplify [Dune_project.default_name] (#2904)

The current implementation finds the minimum twice, perhaps
because `choose` makes no guarantees about what it chooses.
We should just call `min_binding` to get the minimum.

Signed-off-by: Andrey Mokhov <251bbb147316c69f1038239e09718efe08bbf2d1@janestreet.com>
dra27/jbuilder,dra27/jbuilder,dra27/jbuilder,janestreet/jbuilder,janestreet/jbuilder,dra27/jbuilder,janestreet/jbuilder,dra27/jbuilder,janestreet/jbuilder,dra27/jbuilder,janestreet/jbuilder,janestreet/jbuilder