microblaze: remove init_mm

Alexey removed the definition for init_mm from all architectures
but forgot microblaze, which was only recently added.
This fixes the microblaze build by dropping it there as well.

Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/kernel/init_task.c

@@ -18,8 +18,6 @@
 
 static struct signal_struct init_signals = INIT_SIGNALS(init_signals);
 static struct sighand_struct init_sighand = INIT_SIGHAND(init_sighand);
-struct mm_struct init_mm = INIT_MM(init_mm);
-EXPORT_SYMBOL(init_mm);
 
 union thread_union init_thread_union
 	__attribute__((__section__(".data.init_task"))) =