fuzz: revert setup function (#3189)

This can't be used in its current form; revert the entire PR.

Revert "fuzzing: allow setup function to be called (#3175)"

This reverts commit 62451fd3eb.

plugin/pkg/fuzz/do.go

@@ -11,12 +11,7 @@ import (
 )
 
 // Do will fuzz p - used by gofuzz. See Makefile.fuzz for comments and context.
-func Do(p plugin.Handler, fn SetupFunc, data []byte) int {
-	if fn != nil {
-		if err := fn(); err != nil {
-			panic("fuzz: " + err.Error())
-		}
-	}
+func Do(p plugin.Handler, data []byte) int {
 	ctx := context.TODO()
 	r := new(dns.Msg)
 	if err := r.Unpack(data); err != nil {