Use normal `cfg` values in examples

[madsmtm]

We started using cfg_aliases! in #2586, which I guess makes sense from a maintenance perspective (though I'll admit, I'm somewhat against it because it feels like an unnecessary dependency and adds build time).

However, its usage has crept into our examples, which I believe to be a bad idea, as the user will not be having those cfgs, meaning that they cannot directly copy our example code.

So I propose using the normal target_os = "macos"/feature = "x11" values in there.

[kchibisov]

I have a plan to remove all the CFGs all together in 0.31.

[cormacrelf]

One more reason to get rid of config_aliases is that it doesn't work without Cargo, because it relies on all the CARGO_CFG_TARGET_FAMILY (etc) flags being set.

I was writing code to generate fixups for reindeer, and ended up making a recursive evaluator. If it saves you a few minutes, there you go.

https://github.com/cormacrelf/cfg_aliases/tree/winit

or for the buck one, https://github.com/cormacrelf/cfg_aliases/tree/reindeer

android_platform -> target_os = "android"
web_platform -> all(target_family = "wasm", target_os = "unknown")
macos_platform -> target_os = "macos"
ios_platform -> target_os = "ios"
windows_platform -> target_os = "windows"
apple -> any(target_os = "ios", target_os = "macos")
free_unix -> all(unix, not(any(target_os = "ios", target_os = "macos")), not(target_os = "android"), not(target_os = "emscripten"))
redox -> target_os = "redox"
orbital_platform -> target_os = "redox"
x11_platform -> all(feature = "\"x11\"", all(unix, not(any(target_os = "ios", target_os = "macos")), not(target_os = "android"), not(target_os = "emscripten")), not(target_os = "redox"))
wayland_platform -> all(feature = "\"wayland\"", all(unix, not(any(target_os = "ios", target_os = "macos")), not(target_os = "android"), not(target_os = "emscripten")), not(target_os = "redox"))