target-microblaze: Drop unused cpu_mb_close() prototype

Such a function never existed.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>

target-microblaze/cpu.h

@@ -274,7 +274,6 @@ struct CPUMBState {
 
 MicroBlazeCPU *cpu_mb_init(const char *cpu_model);
 int cpu_mb_exec(CPUMBState *s);
-void cpu_mb_close(CPUMBState *s);
 void do_interrupt(CPUMBState *env);
 /* you can call this signal handler from your SIGBUS and SIGSEGV
    signal handlers to inform the virtual CPU of exceptions. non zero