Resolve extra_unused_lifetimes clippy lint
Resolve extra_unused_lifetimes clippy lint

    error: this lifetime isn't used in the impl
       --> serde/src/de/value.rs:607:11
        |
    607 | impl<'de, 'a, E> de::EnumAccess<'de> for StringDeserializer<E>
        |           ^^
        |
        = note: `-D clippy::extra-unused-lifetimes` implied by `-D clippy::all`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#extra_unused_lifetimes

serde-rs/serde