Kernel: Rework kernel-side ELF loading

ELFs are now loaded as MemoryRegions so they don't need special handling
anywhere. This also allows file backed COW optimizations to work. This
was not the case before.

This patch removes now obsolete LoadableELF and unused ELF files from
LibElf.

kernel/include/kernel/Process.h

@@ -22,8 +22,6 @@
 #include <sys/time.h>
 #include <termios.h>
 
-namespace LibELF { class LoadableELF; }
-
 namespace Kernel
 {
 
@@ -269,7 +267,6 @@ namespace Kernel
 
 		OpenFileDescriptorSet m_open_file_descriptors;
 
-		BAN::UniqPtr<LibELF::LoadableELF> m_loadable_elf;
 		BAN::Vector<BAN::UniqPtr<MemoryRegion>> m_mapped_regions;
 
 		pid_t m_sid;