Final clean ups.

It works!  So, yes, need refs/remotes/origin/ prepended to the base_ref,
which will always be a branch for a PR.

* Remove debug lines (set -x, etc).
* No need for pytest here as yet.
* Fall back to requirements.txt if no requirements-dev.txt.

.github/workflows/pr-checks.yml

@@ -38,19 +38,14 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install flake8 pytest
-        if [ -f requirements-dev.txt ]; then pip install -r requirements-dev.txt; fi
+        pip install flake8
+        if [ -f requirements-dev.txt ]; then pip install -r requirements-dev.txt; elif [ -f requirements.txt ]; then pip install -r requirements.txt ; fi
 
     - name: Lint with flake8
       env:
         BASE_REF: ${{github.base_ref}}
 
       run: |
-        # Show all commands as run
-        set -x
-        git branch
-        git log | head -100
-        git diff
         # stop the build if there are Python syntax errors or undefined names, ignore existing 
         git diff "refs/remotes/origin/${BASE_REF}" -- | flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics --diff
         # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide