REGTEST: Add option to use HTX prefixed by the macro 'no-htx'

So some tests have been removed.
diff --git a/reg-tests/server/b00000.vtc b/reg-tests/server/b00000.vtc
index 5fb5c62..831a63d 100644
--- a/reg-tests/server/b00000.vtc
+++ b/reg-tests/server/b00000.vtc
@@ -9,6 +9,7 @@
 haproxy h1 -conf {
     defaults
         mode http
+        ${no-htx} option http-use-htx
         timeout connect 1s
         timeout client  1s
         timeout server  1s