Minor cleanups for staticcheck issues

staticcheck found a couple of minor code cleanup improvements, like
unused variables or an out-of-order defer, mostly in tests.

This patch fixes those problems by making the necessary adjustments.

They're all fairly small, and should not change the logic in any
significant way.

internal/smtpsrv/conn.go

@@ -5,6 +5,7 @@ import (
 	"bytes"
 	"context"
 	"crypto/tls"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -944,7 +945,7 @@ func (c *Conn) runPostDataHook(data []byte) ([]byte, bool, error) {
 
 		// The error contains the last line of stdout, so filters can pass
 		// some rejection information back to the sender.
-		err = fmt.Errorf(lastLine(string(out)))
+		err = errors.New(lastLine(string(out)))
 		return nil, permanent, err
 	}
 

internal/smtpsrv/server.go

@@ -282,7 +282,6 @@ func (s *Server) periodicallyReload() {
 		return
 	}
 
-	//lint:ignore SA1015 This lasts the program's lifetime.
 	for range time.Tick(*reloadEvery) {
 		s.Reload()
 	}