main-loop: Drop qemu_set_fd_handler2

All users are converted to qemu_set_fd_handler now, drop
qemu_set_fd_handler2 and IOHandlerRecord.fd_read_poll.

Signed-off-by: Fam Zheng <famz@redhat.com>
Message-id: 1433400324-7358-9-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
