Remove obsolete comment from sketch compile workflow

This comment referred to a since removed line of the workflow that checked out the `namespace_arduino` branch of
ArduinoCore-API, which has since become unnecessary. The comment was not removed when the configuration was updated and
now might cause confusion.

Author: per1234

.github/workflows/compile-examples.yml

@@ -72,7 +72,6 @@ jobs:
         uses: actions/checkout@v2
         with:
           repository: arduino/ArduinoCore-API
-          # as specified at https://github.com/arduino/ArduinoCore-mbed/blob/master/README.md#installation
           path: ${{ env.ARDUINOCORE_API_STAGING_PATH }}
 
       - name: Install ArduinoCore-API