Remove dev-dependency cty

This can be replaced with using `std::ffi` instead. This was added
in Rust 1.64, but doesn't impact our MSRV as the examples use winit
and glam, which have MSRVS of 1.65 and 1.68.2 respectively for the
versions used at the time of this commit.

Cargo.toml

@@ -41,7 +41,6 @@ version = "0.2.4"
 
 [dev-dependencies]
 cocoa = "0.25.0"
-cty = "0.2.1"
 winit = "0.29"
 sema = "0.1.4"
 png = "0.17"

examples/circle/main.rs

@@ -20,10 +20,10 @@ use std::mem;
 // based on C++
 #[repr(C)]
 #[derive(Debug)]
-pub struct position(cty::c_float, cty::c_float);
+pub struct position(std::ffi::c_float, std::ffi::c_float);
 #[repr(C)]
 #[derive(Debug)]
-pub struct color(cty::c_float, cty::c_float, cty::c_float);
+pub struct color(std::ffi::c_float, std::ffi::c_float, std::ffi::c_float);
 #[repr(C)]
 #[derive(Debug)]
 pub struct AAPLVertex {