kernel: Remove unnecessary includes

Removes unnecessary direct dependencies in some headers and also gets
rid of indirect dependencies that were being relied on to be included.

src/core/hle/kernel/scheduler.h

@@ -8,9 +8,10 @@
 #include <vector>
 #include "common/common_types.h"
 #include "common/thread_queue_list.h"
-#include "core/arm/arm_interface.h"
 #include "core/hle/kernel/thread.h"
 
+class ARM_Interface;
+
 namespace Kernel {
 
 class Scheduler final {