Fix some warnings in examples

[tannal]

Fixs the following warnings.

   Compiling scenes v0.0.0 (C:\Users\tannal\tannalwork\projects\vello\examples\scenes)
warning: the item `Color` is imported redundantly
   --> examples\scenes\src\simple_text.rs:163:29
    |
8   | use vello::peniko::{Blob, Brush, BrushRef, Color, Font, StyleRef};
    |                                            ----- the item `Color` is already imported here
...
163 |         use vello::peniko::{Color, Fill};
    |                             ^^^^^
    |
    = note: `#[warn(unused_imports)]` on by default

warning: the item `PI` is imported redundantly
   --> examples\scenes\src\test_scenes.rs:611:13
    |
86  |     use std::f64::consts::PI;
    |         -------------------- the item `PI` is already imported here
...
611 |         use std::f64::consts::PI;
    |             ^^^^^^^^^^^^^^^^^^^^

   Compiling vello_tests v0.0.0 (C:\Users\tannal\tannalwork\projects\vello\vello_tests)
warning: `scenes` (lib) generated 2 warnings (2 duplicates)
   Compiling with_winit v0.0.0 (C:\Users\tannal\tannalwork\projects\vello\examples\with_winit) 
   Compiling headless v0.0.0 (C:\Users\tannal\tannalwork\projects\vello\examples\headless)     
warning: `scenes` (lib test) generated 2 warnings

[DJMcNab]

Do you have any idea why this wasn't caught by CI before?

I'd like this change to also include the ci fix for that as well, if it's something obvious we missed.

Thanks for sending in the fix!

[tannal]

It's caused by the Rust toolchain version:

• Rust 1.77 reports this error
• The latest Rust 1.80 does not have this issue

https://github.com/tannal/vello/actions/runs/10339098122/job/28618032657#step:4:223

The imported redundantly lint was disabled recently.
rust-lang/rust#121708 (comment)

CI is fine, it's not on us. XD

[DJMcNab]

Thanks for that detailed report. To clarify, these lints are correctly capped when using Vello as a dependency, right? Edit: These aren't even in the dependencies of the vello crate.