Remove unneeded branch of code

Author: wooorm

lib/index.js

@@ -309,9 +309,6 @@ function addProperties(result, properties, schema) {
       ) {
         if (value) {
           result.setAttribute(info.attribute, '')
-        } else {
-          // To do: remove, we create new elements, we don’t mutate existing ones.
-          result.removeAttribute(info.attribute)
         }
       } else if (info.booleanish) {
         result.setAttribute(info.attribute, String(value))