ci: remove old hardhat/minigeth workflows

.github/workflows/test_challenge.yml

-name: Test Challenge
-
-on: pull_request
-
-jobs:
-  unit:
-    name: Challenge on block 13284469
-    runs-on: ubuntu-latest
-    steps:
-    - name: Checkout Code
-      uses: actions/checkout@v3
-      with:
-        submodules: true
-    - name: Install Toolchain
-      run: |
-        sudo apt-get update
-        sudo apt-get -y --no-install-recommends install golang-1.17 nodejs make cmake pkg-config
-        npm install --global pnpm
-    - name: Build
-      run: make libunicorn minigeth_mips minigeth_prefetch mipsevm nodejs
-    - name: Run test challenge
-      run: make test_challenge

.github/workflows/test_challenge_fault.yml

-name: Test Challenge Fault
-
-on: pull_request
-
-jobs:
-  unit:
-    name: Fault injection challenge scenario
-    runs-on: ubuntu-latest
-    steps:
-    - name: Checkout Code
-      uses: actions/checkout@v3
-      with:
-        submodules: true
-    - name: Install Toolchain
-      run: |
-        sudo apt-get update
-        sudo apt-get -y --no-install-recommends install golang-1.17 nodejs make cmake pkg-config
-        npm install --global pnpm
-    - name: Build
-      run: make build
-    - name: Run fault injection challenge scenario
-      run: demo/challenge_fault.sh

.github/workflows/test_challenge_simple.yml

-name: Test Challenge Simple
-
-on: pull_request
-
-jobs:
-  unit:
-    name: Simple challenge scenario
-    runs-on: ubuntu-latest
-    steps:
-    - name: Checkout Code
-      uses: actions/checkout@v3
-      with:
-        submodules: true
-    - name: Install Toolchain
-      run: |
-        sudo apt-get update
-        sudo apt-get -y --no-install-recommends install golang-1.17 nodejs make cmake pkg-config
-        npm install --global pnpm
-    - name: Build
-      run: make build
-    - name: Run simple challenge scenario
-      run: demo/challenge_simple.sh

.github/workflows/test_contracts.yml

-name: Test Contracts
-
-on: pull_request
-
-jobs:
-  unit:
-    name: Contracts work
-    runs-on: ubuntu-latest
-    steps:
-    - name: Checkout Code
-      uses: actions/checkout@v3
-    - name: Install Toolchain (Node and Make)
-      run: |
-        sudo apt-get update
-        sudo apt-get -y --no-install-recommends install nodejs make cmake pkg-config
-        npm install --global pnpm
-    - name: Install Dependencies
-      run: make nodejs
-    - name: Hardhat Test
-      run: make test_contracts

.github/workflows/test_minigeth.yml

-name: Test Minigeth
-
-on: pull_request
-
-jobs:
-  unit:
-    name: minigeth computes correct block transitions
-    runs-on: ubuntu-latest
-    steps:
-    - name: Checkout Code
-      uses: actions/checkout@v3
-      with:
-        submodules: true
-    - name: Install Toolchain
-      run: |
-        sudo apt-get update
-        sudo apt-get -y --no-install-recommends install golang-1.17 make cmake pkg-config
-    - name: Build minigeth
-      run: make minigeth_prefetch
-    - name: Test Minigeth
-      run: make test_minigeth

.github/workflows/test_mipsevm.yml

-name: Test MIPS EVM
-
-on: pull_request
-
-jobs:
-  unit:
-    name: MIPS EVM matches unicorn
-    runs-on: ubuntu-latest
-    steps:
-    - name: Checkout Code
-      uses: actions/checkout@v3
-      with:
-        submodules: true
-    - name: Install Toolchain
-      run: |
-        sudo apt-get update
-        sudo apt-get -y --no-install-recommends install golang-1.17 nodejs make cmake pkg-config
-        npm install --global pnpm
-    - name: Build
-      run: make build
-    - name: Test MIPS EVM
-      run: make test_mipsevm