Kernel: Remove unused header includes in Heap subtree

Author: https://github.com/bgianfo
Commit: https://github.com/SerenityOS/serenity/commit/661809408ee
Pull-request: https://github.com/SerenityOS/serenity/pull/8658

Kernel/Heap/SlabAllocator.cpp

@@ -9,7 +9,6 @@
 #include <Kernel/Heap/SlabAllocator.h>
 #include <Kernel/Heap/kmalloc.h>
 #include <Kernel/Sections.h>
-#include <Kernel/SpinLock.h>
 #include <Kernel/VM/Region.h>
 
 #define SANITIZE_SLABS

Kernel/Heap/kmalloc.cpp

@@ -18,8 +18,6 @@
 #include <Kernel/KSyms.h>
 #include <Kernel/Panic.h>
 #include <Kernel/PerformanceManager.h>
-#include <Kernel/Process.h>
-#include <Kernel/Scheduler.h>
 #include <Kernel/Sections.h>
 #include <Kernel/SpinLock.h>
 #include <Kernel/StdLib.h>