Update CI installation of Rust on macos

Author: alexcrichton

.github/workflows/main.yml

@@ -107,13 +107,7 @@ jobs:
         submodules: true
     - name: Install Rust (rustup)
       run: rustup update ${{ matrix.rust }} --no-self-update && rustup default ${{ matrix.rust }}
-      if: matrix.os != 'macos-latest'
       shell: bash
-    - name: Install Rust (macos)
-      run: |
-        curl https://sh.rustup.rs | sh -s -- -y --default-toolchain nightly
-        echo "##[add-path]$HOME/.cargo/bin"
-      if: matrix.os == 'macos-latest'
     - run: rustup target add ${{ matrix.target }}
     - name: Download compiler-rt reference sources
       run: |