powerpc: Remove old dump_task_* functions

Since Roland's ptrace cleanup starting with commit
f65255e8 ("[POWERPC] Use user_regset
accessors for FP regs"), the dump_task_* functions are no longer being
used.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>