headers: remove sched.h from interrupt.h

After m68k's task_thread_info() doesn't refer to current,
it's possible to remove sched.h from interrupt.h and not break m68k!
Many thanks to Heiko Carstens for allowing this.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c
index 454cdb4..039270b 100644
--- a/arch/um/kernel/irq.c
+++ b/arch/um/kernel/irq.c
@@ -10,6 +10,7 @@
 #include "linux/interrupt.h"
 #include "linux/kernel_stat.h"
 #include "linux/module.h"
+#include "linux/sched.h"
 #include "linux/seq_file.h"
 #include "as-layout.h"
 #include "kern_util.h"