tty: jsm: remove unused members from struct board_ops

tty: jsm: remove unused members from struct board_ops

clang-struct [1] found board_ops::get_uart_bytes_left() and
::send_immediate_char() unused.

Both are only set but never called. And it has been like that since the
git history, so drop both the members along with the cls+neo
implementations.

[1] https://github.com/jirislaby/clang-struct

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20231121103626.17772-4-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>