[SPARC64]: Kill show_stackframe{,32}().

Noticed via sparse:

arch/sparc64/kernel/process.c:215:6: warning: symbol 'show_stackframe' was not declared. Should it be static?
arch/sparc64/kernel/process.c:243:6: warning: symbol 'show_stackframe32' was not declared. Should it be static?

It is totally unused.

Signed-off-by: David S. Miller <davem@davemloft.net>