Rm step for installing musl-tool in job test

The job `test` for target `x86_64-unknown-linux-musl` requires
`musl-tool` since there is no pre-built binary present for that target
and thus `cargo-binstall` automatically fall back to `cargo-build`.

Currently, the test for it also failed because `libssl-1.1` is not
present.

However, since this will be fixed once a new release of `cargo-binstall`
is published, this step should not be present.

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

.github/workflows/rust.yml

@@ -160,10 +160,6 @@ jobs:
         target:  ${{ matrix.target }}
         override: true
 
-    - name: Install musl-tools
-      if: ${{ matrix.target == 'x86_64-unknown-linux-musl' }}
-      run: sudo apt-get install -y musl-tools
-
     - uses: actions/download-artifact@v2
       with:
         name: cargo-binstall-${{ matrix.target }}.${{ matrix.archive }}