[kernel] Remove explicit allocator passing

Many kernel objects had to keep a hold of refrences to allocators in
order to pass them on down the call chain. Remove those explicit
refrences and use `operator new`, `operator delete`, and define new
`kalloc` and `kfree`.

Also remove `slab_allocator` and replace it with a new mixin for slab
allocation, `slab_allocated`, that overrides `operator new` and
`operator free` for its subclass.

Remove some no longer used related headers, `buddy_allocator.h` and
`address_manager.h`

Tags: memory

src/kernel/objects/kobject.cpp

@@ -12,7 +12,6 @@ static j6_koid_t next_koid;
 kobject::kobject(type t, j6_signal_t signals) :
 	m_koid(koid_generate(t)),
 	m_signals(signals),
-	m_observers(g_kernel_heap),
 	m_handle_count(0)
 {}