Use explicit iteration instead of `all()` in `process_obligation()`.
Use explicit iteration instead of `all()` in `process_obligation()`.

Amazingly enough, this is a 3.5% instruction count win on `keccak`.

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust