Validate number of entries in `x-enum-varnames`

[jamietanna]

diff --git examples/extensions/xenumvarnames/api.yaml examples/extensions/xenumvarnames/api.yaml
index 5601f4a5..8bdd308d 100644
--- examples/extensions/xenumvarnames/api.yaml
+++ examples/extensions/xenumvarnames/api.yaml
@@ -16,4 +16,3 @@ components:
         - EXP
       x-enum-varnames:
         - Active
-        - Expired
diff --git examples/extensions/xenumvarnames/gen.go examples/extensions/xenumvarnames/gen.go
index 6b919353..a6137d39 100644
--- examples/extensions/xenumvarnames/gen.go
+++ examples/extensions/xenumvarnames/gen.go
@@ -5,14 +5,14 @@ package xenumvarnames
 
 // Defines values for ClientType.
 const (
-       ACT ClientType = "ACT"
-       EXP ClientType = "EXP"
+       ClientTypeACT ClientType = "ACT"
+       ClientTypeEXP ClientType = "EXP"
 )
 
 // Defines values for ClientTypeWithExtension.
 const (
-       Active  ClientTypeWithExtension = "ACT"
-       Expired ClientTypeWithExtension = "EXP"
+       ClientTypeWithExtensionActive ClientTypeWithExtension = "ACT"
+       ClientTypeWithExtensionEXP    ClientTypeWithExtension = "EXP"
 )
 
 // ClientType defines model for ClientType.