Remove pattern in trait's method signature
Remove pattern in trait's method signature

This use of `mut` was nonsensical for now, but is proposed to be
disallowed by rustc in the future (as a bugfix in Rust).

rust-num/num-traits,DonSheddow/num,rust-num/num-integer,DonSheddow/num,koverstreet/num,rust-lang/num,rust-lang/num,rust-num/num,rust-num/num-bigint,rust-num/num,rust-num/num-integer,koverstreet/num,vks/num,rust-num/num-bigint,rust-num/num-traits,vks/num