Kernel: Fully remove sys_alloc and sys_free

I could delete the whole FixedWidthAllocator as it was now obsolete.
GeneralAllocator is still used by kmalloc. Kmalloc cannot actually
use it since, GeneralAllocator depends on SpinLock and kmalloc runs
without interrupts.

kernel/CMakeLists.txt

@@ -32,7 +32,6 @@ set(KERNEL_SOURCES
 	kernel/Input/PS2Keymap.cpp
 	kernel/InterruptController.cpp
 	kernel/kernel.cpp
-	kernel/Memory/FixedWidthAllocator.cpp
 	kernel/Memory/GeneralAllocator.cpp
 	kernel/Memory/Heap.cpp
 	kernel/Memory/kmalloc.cpp