Remove irrelevant comment from CI workflow

This comment was a leftover from a previous time when the `namespace` branch of ArduinoCore-API was specified for use
with the arduino:mbed boards platform.

Author: per1234

.github/workflows/compile-examples.yml

@@ -194,7 +194,6 @@ 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