chore(volo-grpc): fix clippy rule needless_lifetimes

[yukiiiteru]

Motivation

error: the following explicit lifetimes could be elided: 'a
   --> volo-grpc/src/metadata/key.rs:207:6
    |
207 | impl<'a, VE: ValueEncoding> PartialEq<MetadataKey<VE>> for &'a MetadataKey<VE> {
    |      ^^                                                     ^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes
    = note: `-D clippy::needless-lifetimes` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::needless_lifetimes)]`
help: elide the lifetimes
    |
207 - impl<'a, VE: ValueEncoding> PartialEq<MetadataKey<VE>> for &'a MetadataKey<VE> {
207 + impl<VE: ValueEncoding> PartialEq<MetadataKey<VE>> for &MetadataKey<VE> {
    |

Solution

Fix them