remove pre.mode

docs/Reference.md

@@ -768,10 +768,6 @@ those methods are called in parallel. `pre` can be assigned a mixed array of:
 - objects with:
     - `method` - the function to call (or short-hand helper string as described below). The function signature is defined by the `type` options.
     - `assign` - key name to assign the result of the function to within `request.pre`.
-    - `mode` - the calling order of the function. Available values:
-        - `'serial'` - serial methods are executed after all the `'parallel'` methods in the order listed. This is the default value.
-        - `'parallel'` - all parallel methods are executed first in parallel before any serial method. The first to return an error response
-          will exist the set.
     - `type` - the method signature by specifying one of the following (defualts to `'pre'`):
         - `'pre'` - the function signature is `function(request, next)` where:
             - `request` - the incoming `request` object.