Revert "Implement notifies for transfer plugin (#3972)" (#3995)

This reverts commit 68f1dd5ddf.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

plugin/file/secondary_test.go

@@ -11,6 +11,10 @@ import (
 	"github.com/miekg/dns"
 )
 
+// TODO(miek): should test notifies as well, ie start test server (a real coredns one)...
+// setup other test server that sends notify, see if CoreDNS comes calling for a zone
+// transfer
+
 func TestLess(t *testing.T) {
 	const (
 		min  = 0