Remove quote dependency

[BD103]

quote's only usage is returning a unit () statement. This behavior can be accomplished by calling TokenStream::new, which returns an empty token stream.

This does change the generated output, but it still accomplishes the same result.

// stretch_your_legs.rs

// Before
fn main() {
    ();
}

// After
fn main() {

}

Unfortunately it only removes quote as an immediate dependency. syn still dependends on quote, even when I reduced the enabled features. I'm pretty sure this is a bug (on this line), but there is nothing that can be done in this PR.

[BD103]

I just created dtolnay/syn#1608 and it was merged, so quote should fully be removed as a dependency next time syn releases. All that needs to be done is to cargo update and specify a minimum syn version to 2.0.56.

[BD103]

Ok, that's about as much as I can do. quote is still being included in the lockfile for reasons I don't understand, but it is no longer being built by cargo so it's good enough.

[taiki-e]

quote is still being included in the lockfile for reasons I don't understand

I think this is due to rust-lang/cargo#10801.

[radekvit]

Thank you for the contribution, this is a nice improvement.

I never thought I'd get PRs making this compile faster, but here we are.