Remove PAM from auth dropdown when unavailable (#13276)

Signed-off-by: jolheiser <john.olheiser@gmail.com>

modules/auth/pam/pam_stub.go

@@ -10,6 +10,9 @@ import (
 	"errors"
 )
 
+// Supported is false when built without PAM
+var Supported = false
+
 // Auth not supported lack of pam tag
 func Auth(serviceName, userName, passwd string) (string, error) {
 	return "", errors.New("PAM not supported")