powerpc/xmon: remove unused ppc_parse_cpu() declaration

ppc_parse_cpu() has been removed since
commit 5b102782c7f4 ("powerpc/xmon: Enable disassembly
files (compilation changes)"), so remove it.

Signed-off-by: Gaosheng Cui <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/xmon/ppc.h

···
 extern const struct powerpc_macro powerpc_macros[];
 extern const int powerpc_num_macros;
 
-extern ppc_cpu_t ppc_parse_cpu (ppc_cpu_t, ppc_cpu_t *, const char *);
-
 static inline long
 ppc_optional_operand_value (const struct powerpc_operand *operand)
 {