Remove unused error

imaputils/connection.go

@@ -10,7 +10,6 @@ import (
 	"github.com/emersion/go-imap/client"
 )
 
-var ErrMissingConfig = errors.New("missing configuration stanza")
 var ErrUnencrypted = errors.New("the connection is unencrypted")
 
 type IMAPConnection struct {