hw/char: Remove unused serial_set_frequency

serial_set_frequnecy has been unused since it was added in 2009:
  038eaf82c8 ("serial: Add interface to set reference oscillator frequency")

It looks like the 'baudbase' is now a property anyway so the wrapper
isn't needed.

Remove it.

Signed-off-by: Dr. David Alan Gilbert <dave@treblig.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/char/serial.c

@@ -951,13 +951,6 @@ static void serial_unrealize(DeviceState *dev)
     qemu_unregister_reset(serial_reset, s);
 }
 
-/* Change the main reference oscillator frequency. */
-void serial_set_frequency(SerialState *s, uint32_t frequency)
-{
-    s->baudbase = frequency;
-    serial_update_parameters(s);
-}
-
 const MemoryRegionOps serial_io_ops = {
     .read = serial_ioport_read,
     .write = serial_ioport_write,

include/hw/char/serial.h

@@ -93,8 +93,6 @@ struct SerialMM {
 extern const VMStateDescription vmstate_serial;
 extern const MemoryRegionOps serial_io_ops;
 
-void serial_set_frequency(SerialState *s, uint32_t frequency);
-
 #define TYPE_SERIAL "serial"
 OBJECT_DECLARE_SIMPLE_TYPE(SerialState, SERIAL)