Rollup merge of #149010 - Zalathar:wasm32-bare, r=jieyouxu

compiletest: Remove the "wasm32-bare" alias for `wasm32-unknown-unknown`

- Follow-up to rust-lang/rust#148969

This "wasm32-bare" alias, understood by compiletest's `//@ ignore-wasm32-bare` and `//@ only-wasm32-bare` directives, dates all the way back to the original introduction of the `wasm32-unknown-unknown` target in rust-lang/rust#45905.

But there is no compelling reason to use an alias instead of the full target name.

r? jieyouxu

Author: Zalathar

src/tests/directives.md

@@ -141,7 +141,6 @@ Some examples of `X` in `ignore-X` or `only-X`:
 - OS: `android`, `emscripten`, `freebsd`, `ios`, `linux`, `macos`, `windows`,
   ...
 - Environment (fourth word of the target triple): `gnu`, `msvc`, `musl`
-- WASM: `wasm32-bare` matches `wasm32-unknown-unknown`.
 - Pointer width: `32bit`, `64bit`
 - Endianness: `endian-big`
 - Stage: `stage1`, `stage2`