Rename Header to HulkHeader

src/hello/hello.d

@@ -7,7 +7,7 @@ import uefi;
 import console = hello.console;
 import scratch = hello.scratch;
 import hulk.bootinfo;
-import hulk.header : HulkHeader = Header;
+import hulk.header;
 import hos.page_table;
 import hos.cpu;
 import hos.memory;