All uses of sb1250_time_init() have been removed by
commit d527eef5 ("[MIPS] Sibyte: Finish conversion to modern
time APIs."), so remove the orphan declaration.

The comments about sb1250_time_init() is useless in arch_init_irq(),
so remove these comments.
Signed-off-by: NGaosheng Cui <cuigaosheng1@huawei.com>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: NThomas Bogendoerfer <tsbogend@alpha.franken.de>