gpg: Fix wrong use of FD2INT with iobuf_fdopen_nc.

* g10/decrypt.c (decrypt_message_fd): Use INPUT_FD directly.
* g10/encrypt.c (encrypt_crypt): Use FILEFD directly.

Before 8402815d, original code was with iobuf_open_fd_or_name, which
used gnupg_fd_t for the file descriptor (FD2INT was relevant at that
time). After the change, because it's not gnupg_fd_t but int, use of
FD2INT is irrelevant.

• Fixes-commit: 8402815d8e0e04a44362968f88b3d484d2395402
• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>