microblaze: mmu: Delete flip_um fn prototype

This is not implemented or used.

Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

target-microblaze/mmu.h

@@ -82,7 +82,6 @@ struct microblaze_mmu_lookup
     } err;
 };
 
-void mmu_flip_um(CPUMBState *env, unsigned int um);
 unsigned int mmu_translate(struct microblaze_mmu *mmu,
                            struct microblaze_mmu_lookup *lu,
                            target_ulong vaddr, int rw, int mmu_idx);