Auto merge of rust-lang#16851 - lnicola:ubuntu-20.04, r=lnicola

internal: Build releases on Ubuntu 20.04

Closes rust-lang#16793

Author: bors

.github/workflows/release.yaml

@@ -36,7 +36,6 @@ jobs:
           - os: ubuntu-20.04
             target: x86_64-unknown-linux-gnu
             code-target: linux-x64
-            container: ubuntu:18.04
           - os: ubuntu-20.04
             target: aarch64-unknown-linux-gnu
             code-target: linux-arm64
@@ -63,14 +62,6 @@ jobs:
         with:
           fetch-depth: ${{ env.FETCH_DEPTH }}
 
-      - name: Install toolchain dependencies
-        if: matrix.container == 'ubuntu:18.04'
-        shell: bash
-        run: |
-          apt-get update && apt-get install -y build-essential curl
-          curl --proto '=https' --tlsv1.2 --retry 10 --retry-connrefused -fsSL "https://sh.rustup.rs" | sh -s -- --profile minimal --default-toolchain none -y
-          echo "${CARGO_HOME:-$HOME/.cargo}/bin" >> $GITHUB_PATH
-
       - name: Install Rust toolchain
         run: |
           rustup update --no-self-update stable