Remove the recently added "Limit $PATH" step

I had put that step in the Cygwin workflow for purposes of
experimentation, and it seemed to make clearer what is going on,
but really it does the opposite: it's deceptive because Cygwin uses
other logic to set its PATH. So this step is unnecessary and
ineffective at doing what it appears to do.

Author: EliahKagan

.github/workflows/cygwin-test.yml

@@ -33,10 +33,6 @@ jobs:
       with:
         packages: python39 python39-pip python39-virtualenv git
 
-    - name: Limit $PATH to Cygwin
-      run: |
-        echo 'C:\cygwin\bin' > "$GITHUB_PATH"  # Overwrite it with just this.
-
     - name: Special configuration for Cygwin's git
       run: |
         git config --global --add safe.directory "$(pwd)"