reads correctly unqualified system names (#1438)

This is a minor bug fix, that enables proper reading of unqualified
system names in Primus, so that `Primus.System.Repository.get
~package:"bap" "foo:xxxx` gets `foo:xxx` not `bap:foo\:xxx`.

Author: ivg

lib/bap_primus/bap_primus_system.ml

@@ -53,7 +53,7 @@ module Repository = struct
     | None -> invalid_argf "Unknown system %s" (Name.show name) ()
 
   let get ?package name =
-    require @@ Name.create ?package name
+    require @@ Name.read ?package name
 
   let find = Hashtbl.find self