More cleanup (#967)

Changes:
* update maven-wrapper to 3.3.0
* do not override parent versions
* use properties where appropriate

.mvn/wrapper/maven-wrapper.properties

@@ -6,13 +6,12 @@
 # "License"); you may not use this file except in compliance
 # with the License.  You may obtain a copy of the License at
 #
-#   https://www.apache.org/licenses/LICENSE-2.0
+#   http://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing,
 # software distributed under the License is distributed on an
 # "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 # KIND, either express or implied.  See the License for the
 # specific language governing permissions and limitations
 # under the License.
-distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.8.7/apache-maven-3.8.7-bin.zip
-wrapperUrl=https://repo.maven.apache.org/maven2/org/apache/maven/wrapper/maven-wrapper/3.1.1/maven-wrapper-3.1.1.jar
+distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.8.8/apache-maven-3.8.8-bin.zip