Delete #[cfg_attr(wasi, path = "backend/wasi/mod.rs")]

[dtolnay]

Closes #1539.

As far as I can tell, nothing in build.rs enables cfg(wasi), unlike cfg(libc) and cfg(linux_raw).

Enabling it manually results in:

bytecodealliance:rustix$  RUSTFLAGS=--cfg=wasi cargo check --target=wasm32-wasip2

warning: unused attribute
   --> src/lib.rs:197:18
    |
197 | #[cfg_attr(wasi, path = "backend/wasi/mod.rs")]
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
    |
note: attribute also specified here
   --> src/lib.rs:195:18
    |
195 | #[cfg_attr(libc, path = "backend/libc/mod.rs")]
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: `#[warn(unused_attributes)]` (part of `#[warn(unused)]`) on by default

[sunfishcode]

Thanks! This was part of an early experiment that I or someone else may revisit some day, but it makes sense to fully remove for now.

[sunfishcode]

This is now released in rustix 1.1.3.