Simplify CI workflow.

.github/workflows/main.yaml

@@ -24,8 +24,8 @@ jobs:
         sudo add-apt-repository 'deb http://ppa.launchpad.net/sri-csl/formal-methods/ubuntu bionic main'
         sudo apt-get update
         sudo apt-get install yices2
-        pip install setuptools setuptools_scm wheel coverage codecov yowasp-yosys nmigen-yosys
-        pip install -e .
+        pip install coverage codecov yowasp-yosys
+        pip install -e .[builtin-yosys]
     - name: Preserve wasmtime cache
       uses: actions/cache@v1
       with:
@@ -48,7 +48,6 @@ jobs:
         uses: actions/setup-python@v2
       - name: Install dependencies
         run: |
-          python -m pip install --upgrade setuptools setuptools_scm wheel
           pip install -r docs/requirements.txt
           pip install -e .
       - name: Build documentation