IR model: stop trying to play with word joiners (U+2060).

It breaks cut and paste in the HTML renderer and other
renderers have to ignore it.

Closes #620.

src/document/generator.ml

@@ -44,7 +44,7 @@ let make_name_from_path { Url.Path.name; parent; _ } =
 let label t ppf =
   match t with
   | Odoc_model.Lang.TypeExpr.Label s -> O.pf ppf "%s" s
-  | Optional s -> O.pf ppf "?%t%s" (O.entity "#8288") s
+  | Optional s -> O.pf ppf "?%s" s
 
 let tag tag t ppf = O.pf ppf "@{<%s>%t@}" tag t
 

src/latex/generator.ml

@@ -111,7 +111,6 @@ let list kind pp ppf x =
 let escape_entity = function
   | "#45" -> "-"
   | "gt" -> ">"
-  | "#8288" -> ""
   | s -> s
 
 let filter_map f x =

src/manpage/generator.ml

@@ -260,7 +260,6 @@ let entity e =
   match e with
   | "#45" -> escaped "\\-"
   | "gt" -> str ">"
-  | "#8288" -> noop
   | s -> str "&%s;" s
 
 (* Should hopefully make people notice and report *)