CI: Use rust-toolchain

Latest nightly broke a dependency. Need to wait for it to be fixed. Pin the
toolchain for now.

.github/workflows/build_rpi3.yml

@@ -31,11 +31,6 @@ jobs:
           ruby-version: "2.7"
       - name: Set up Rust nightly
         run: |
-          rm rust-toolchain
-          rustup self update
-          rustup toolchain install nightly --component llvm-tools-preview
-          rustup default nightly
-          rustup target add aarch64-unknown-none-softfloat
           cargo install cargo-binutils
       - name: Set up Ruby
         run: |

.github/workflows/build_rpi4.yml

@@ -31,11 +31,6 @@ jobs:
           ruby-version: "2.7"
       - name: Set up Rust nightly
         run: |
-          rm rust-toolchain
-          rustup self update
-          rustup toolchain install nightly --component llvm-tools-preview
-          rustup default nightly
-          rustup target add aarch64-unknown-none-softfloat
           cargo install cargo-binutils
       - name: Set up Ruby
         run: |

.github/workflows/sanity.yml

@@ -31,13 +31,6 @@ jobs:
       - name: Set up Prettier
         run: |
           npm install prettier
-      - name: Set up Rust nightly
-        run: |
-          rm rust-toolchain
-          rustup self update
-          rustup toolchain install nightly --component rustfmt clippy
-          rustup default nightly
-          rustup target add aarch64-unknown-none-softfloat
       - name: Setup misspell
         run: |
           curl -L -o ./install-misspell.sh https://git.io/misspell

.github/workflows/test_integration.yml

@@ -31,11 +31,6 @@ jobs:
           ruby-version: "2.7"
       - name: Set up Rust nightly
         run: |
-          rm rust-toolchain
-          rustup self update
-          rustup toolchain install nightly --component llvm-tools-preview
-          rustup default nightly
-          rustup target add aarch64-unknown-none-softfloat
           cargo install cargo-binutils
       - name: Set up Ruby
         run: |

.github/workflows/test_unit.yml

@@ -31,11 +31,6 @@ jobs:
           ruby-version: "2.7"
       - name: Set up Rust nightly
         run: |
-          rm rust-toolchain
-          rustup self update
-          rustup toolchain install nightly --component llvm-tools-preview
-          rustup default nightly
-          rustup target add aarch64-unknown-none-softfloat
           cargo install cargo-binutils
       - name: Set up Ruby
         run: |

.github/workflows/test_xtra.yml

@@ -31,11 +31,6 @@ jobs:
           ruby-version: "2.7"
       - name: Set up Rust nightly
         run: |
-          rm rust-toolchain
-          rustup self update
-          rustup toolchain install nightly --component llvm-tools-preview
-          rustup default nightly
-          rustup target add aarch64-unknown-none-softfloat
           cargo install cargo-binutils
       - name: Set up Ruby
         run: |