Kernel: Remove kernel processes

Kernel can just use raw threads, pretty muchs the only thing that
process provides is syscalls which kernel threads of course don't
need.

Also this makes init process have pid 1 :D

kernel/kernel/kernel.cpp

@@ -199,7 +199,8 @@ extern "C" void kernel_main(uint32_t boot_magic, uint32_t boot_info)
 	Processor::wait_until_processors_ready();
 	MUST(Processor::scheduler().initialize());
 
-	Process::create_kernel(init2, nullptr);
+	auto* init_thread = MUST(Thread::create_kernel(init2, nullptr));
+	MUST(Processor::scheduler().add_thread(init_thread));
 	Processor::yield();
 
 	ASSERT_NOT_REACHED();