gpg: Fix printing keyserver URLs and notation data.

* g10/keylist.c (show_keyserver_url): Print to 'fp', not to 'stdout'.
(show_notation): Likewise.

Fixes the fact that if mode == -1, all text except for the labels is
written to the tty, but the label is written to stdout, which is
buffered.

• Signed-off-by: Justus Winter <justus@g10code.com>