undo a couple of retroactive annotations where older compilers can't handle the constraint on them

Author: mattpolzin

Sources/OpenAPIKit/Either/Either+Validatable.swift

@@ -7,4 +7,4 @@
 
 import OpenAPIKitCore
 
-extension Either: @retroactive Validatable where A: Validatable, B: Validatable {}
+extension Either: Validatable where A: Validatable, B: Validatable {}

Sources/OpenAPIKit/OrderedDictionary+Validatable.swift

@@ -7,4 +7,4 @@
 
 import OpenAPIKitCore
 
-extension OrderedDictionary: @retroactive Validatable where Value: Validatable {}
+extension OrderedDictionary: Validatable where Value: Validatable {}