Auto merge of #467 - JustForFun88:remove_cross_toml, r=Amanieu

Migrate from `actions-rs/toolchain@v1` to `dtolnay/rust-toolchain@master` and remove `Cross.toml`

This PR replace the usage of [actions-rs/toolchain@v1](https://github.com/actions-rs/toolchain) with [dtolnay/rust-toolchain](https://github.com/dtolnay/rust-toolchain) as it is no longer maintained and uses the deprecated GitHub Actions API. The [dtolnay/rust-toolchain](https://github.com/dtolnay/rust-toolchain) provides similar functionality and also provides some additional features such as colored output.

Regarding the `Cross.toml` file, it is no longer needed after merging rust-lang/rust#115267.

.github/workflows/rust.yml

@@ -37,10 +37,9 @@ jobs:
     needs: basics
     steps:
     - uses: actions/checkout@v3
-    - uses: actions-rs/toolchain@v1
+    - uses: dtolnay/rust-toolchain@master
       with:
         toolchain: ${{ matrix.channel }}
-        override: true
     - env:
         TARGET: ${{ matrix.target }}
         CHANNEL: ${{ matrix.channel }}