Remove dead code

lib.js

@@ -143,30 +143,6 @@ function searchFeaturesInDocument (document, query) {
   return document
 }
 
-function featureToString (feature) {
-  /*
-   * Turn into feature object into category>type>subtype String
-   */
-
-  let category = feature.category
-  let type = feature.type
-  let subtype = feature.subtype
-
-  let ret = ''
-
-  if (category !== undefined) {
-    ret = ret.concat(category)
-  }
-  if (type !== undefined) {
-    ret = ret.concat(' > ', type)
-  }
-  if (subtype !== undefined) {
-    ret = ret.concat(' > ', subtype)
-  }
-
-  return ret
-}
-
 function featureGlossary (objs) {
   /*
    * Turn list of documents objects into a glossary set