elf.h: drop Elf*_Chdr (libelf.h defines its own; conflicting types)

The Chdr structs were added speculatively but libelf's <libelf.h> defines its
own Elf32_Chdr/Elf64_Chdr, causing 'conflicting types'. gelf.h only needed
Sword/Versym/Lib/Relr, which remain.

src/header/elf/cbindgen.toml

@@ -67,18 +67,6 @@ typedef struct {
   uint32_t l_version;
   uint32_t l_flags;
 } Elf64_Lib;
-
-typedef struct {
-  uint32_t ch_type;
-  uint32_t ch_size;
-  uint32_t ch_addralign;
-} Elf32_Chdr;
-typedef struct {
-  uint32_t ch_type;
-  uint32_t ch_reserved;
-  uint64_t ch_size;
-  uint64_t ch_addralign;
-} Elf64_Chdr;
 """
 include_guard = "_ELF_H"
 language = "C"