doc: remove required link
@@ -224,7 +224,6 @@ copied by the `spec` plugin just before):
- [type](type/) type checking (CORBA types) with enum functionality
- [mathcheck](mathcheck/) by mathematical expressions using key values as operands
- [conditionals](conditionals/) by using if-then-else like statements
-- [required](required/) rejects non-required keys
- [date](date/) validates date and time data
- [range](range/) checks if a value is within a given range
- [reference](reference/) checks if a value is a valid reference to another key
