Removed True and False constraints from reference

Author: edefimov

reference/constraints.rst

@@ -9,11 +9,8 @@ Validation Constraints Reference
    constraints/Blank
    constraints/NotNull
    constraints/IsNull
-   constraints/Null
    constraints/IsTrue
-   constraints/True
    constraints/IsFalse
-   constraints/False
    constraints/Type
 
    constraints/Email