Remove work-around for Rust issue 16597.
Remove work-around for Rust issue 16597.

https://github.com/rust-lang/rust/issues/16597

frewsxcv/rust-cssparser,notriddle/rust-cssparser,disjukr/rust-cssparser,servo/rust-cssparser,tempbottle/rust-cssparser,frewsxcv/rust-cssparser,disjukr/rust-cssparser,notriddle/rust-cssparser,servo/rust-cssparser,tempbottle/rust-cssparser