Remove redundant minimalMavenBuildVersion override

[DomGarguilo]

Remove the local minimalMavenBuildVersion property from the pom.

Apache parent pom version 36 added the same Maven 3.9 minimum via a PR I made at apache/maven-apache-parent#533. We use version 37 which includes this so the override is now redundant and we can remove it.

Refs:

• Update minimum maven version to match current stable version (3.6.3 -> 3.9) maven-apache-parent#533
• https://github.com/apache/maven-apache-parent/releases#release-apache-36

[DomGarguilo]

Verified the effective POM shows the expected 3.9 after removing the local override:

mvn help:effective-pom -Doutput=/tmp/accumulo-effective-pom.xml -DskipTests
grep -n "minimalMavenBuildVersion" /tmp/accumulo-effective-pom.xml

[ctubbsii]

This is fine, but should be applied to 2.1 first and merged to main. I try to keep the build stuff up-to-date on all our active branches, because it helps ensure a smooth release, rather than just apply this stuff to main.