rust: update bindgen to 0.69.4; remove custom type modifications

rust: update bindgen to 0.69.4; remove custom type modifications

This updates rust-bindgen to version 0.69.4 which includes the patch
199bee441ad0: "try to avoid #[repr(packed)] when align is needed". With
this patch, bindgen generates code that is both ABI-correct and can be
compiled by rustc, for 3 bcachefs types:

- bkey
- bch_extent_crc32
- bch_extent_ptr

This allows us to remove the custom treatment for these three types.

Signed-off-by: Thomas Bertschinger <tahbertschinger@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>