Contracts have unused lifetime by default

[SkymanOne]

Summary

If we create a contract template, clippy complains about unused lifetime at [ink::contract] macro. The warning is suppressed in CI, and has no affect on performance (not tested), but it definitely affect developer experience.

Illustration

Reproduction

1. Checkout ink4.0
2. Create a template smart contract with cargo contract new <name>
3. Run cargo clippy

The output should look similar to:

warning: this lifetime isn't used in the impl
 --> lib.rs:3:1
  |
3 | #[ink::contract]
  | ^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(clippy::extra_unused_lifetimes)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#extra_unused_lifetimes
  = note: this warning originates in the attribute macro `ink::contract` (in Nightly builds, run with -Z macro-backtrace for more info)

[SkymanOne]

Closing as seems to be fixed in #1508