hw/i386: Remove obsolete LoadStateHandler::load_state_old handlers

hw/i386: Remove obsolete LoadStateHandler::load_state_old handlers

These devices implemented their load_state_old() handler 10 years
ago, previous to QEMU v0.12.
Since commit cc425b5ddf removed the pc-0.10 and pc-0.11 machines,
we can drop this code.

Note: the mips_r4k machine started to use the i8254 device just
after QEMU v0.5.0, but the MIPS machine types are not versioned,
so there is no migration compatibility issue removing this handler.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>