Kernel: Remove the kmalloc_eternal heap :^)

This was a premature optimization from the early days of SerenityOS.
The eternal heap was a simple bump pointer allocator over a static
byte array. My original idea was to avoid heap fragmentation and improve
data locality, but both ideas were rooted in cargo culting, not data.

We would reserve 4 MiB at boot and only ended up using ~256 KiB, wasting
the rest.

This patch replaces all kmalloc_eternal() usage by regular kmalloc().

Kernel/Graphics/Intel/NativeGraphicsAdapter.h

@@ -47,7 +47,6 @@ enum RegisterIndex {
 
 class IntelNativeGraphicsAdapter final
     : public VGACompatibleAdapter {
-    AK_MAKE_ETERNAL
 public:
     struct PLLSettings {
         bool is_valid() const { return (n != 0 && m1 != 0 && m2 != 0 && p1 != 0 && p2 != 0); }