Remove debug message about schema validation

Removed debug message printed at the end of the validation for
each scenario. This spammed output and it is not really needed because
we already print when we start validation and if it fails.

lib/molecule/config.py

@@ -421,9 +421,6 @@ def _validate(self):
             msg = f"Failed to validate {self.molecule_file}\n\n{errors}"
             util.sysexit_with_message(msg)
 
-        msg = "Validation completed successfully."
-        LOG.debug(msg)
-
 
 def molecule_directory(path):
     """Return directory of the current scenario."""