[file_packager] Remove handleError. NFC

The last usage was removed in emscripten-core#24904 but I forgot to remove the function
itself.

Author: sbc100

tools/file_packager.py

@@ -1008,10 +1008,6 @@ def generate_js(data_target, data_files, metadata):
             Module['setStatus']?.('Downloading data...');
             return iterate();
           });
-      };
-
-      function handleError(error) {
-        console.error('package error:', error);
       };\n''' % {'node_support_code': node_support_code}
 
     code += '''