ppc: Remove duplicate export of get_wchan

The arch/powerpc version of process.c exports get_wchan itself. When
I moved ARCH=ppc over to using arch/powerpc/kernel/process.c the
get_wchan export in arch/ppc/kernel/ppc_ksyms.c became redundant, so
remove it.

Signed-off-by: Paul Mackerras <[e-mail]>
(cherry picked from 9871166ad692121d6b944159ef3f053570158ea8 commit)

arch/ppc/kernel/ppc_ksyms.c

···
 EXPORT_SYMBOL(timer_interrupt);
 EXPORT_SYMBOL(irq_desc);
 EXPORT_SYMBOL(tb_ticks_per_jiffy);
-EXPORT_SYMBOL(get_wchan);
 EXPORT_SYMBOL(console_drivers);
 #ifdef CONFIG_XMON
 EXPORT_SYMBOL(xmon);