Remove merge_parquet_pr.py and clean up LICENSE (#484)

At Iceberg we've been cleaning up some LICENSES.
Since the `merge_parquet_pr.py` is not used anymore with
the GitHub workflow, I think it would be good to clean
this up from the repository and source release.

Author: Fokko

LICENSE

@@ -201,13 +201,3 @@
    See the License for the specific language governing permissions and
    limitations under the License.
 
---------------------------------------------------------------------------------
-
-This product includes code from Apache Spark.
-
-* dev/merge_parquet_pr.py is based on Spark's dev/merge_spark_pr.py
-
-Copyright: 2014 The Apache Software Foundation.
-Home page: https://spark.apache.org/
-License: http://www.apache.org/licenses/LICENSE-2.0
-