Remove duplicate dependency declarations rejected by Maven 3.10

[vharseko]

Problem

The build-maven jobs started failing on open PRs (#251, #226) before compilation, while reading the POMs:

[ERROR] 'dependencies.dependency.(groupId:artifactId:type:classifier)' must be unique: com.fasterxml.jackson.core:jackson-core:jar -> duplicate declaration of version (?) @ line 204, column 21
[ERROR] 'dependencies.dependency.(groupId:artifactId:type:classifier)' must be unique: org.osgi:org.osgi.util.promise:jar -> duplicate declaration of version (?) @ line 92, column 21
[ERROR] 'dependencies.dependency.(groupId:artifactId:type:classifier)' must be unique: org.osgi:org.osgi.util.function:jar -> duplicate declaration of version (?) @ line 97, column 21

Which job fails depends only on which runner image it lands on: the ubuntu-24.04 image 20261004.327 ships Maven 3.10.0, which rejects a repeated <dependency> declaration, while the previous image 20260927.320 (Maven 3.9.16) only warns about it. The duplicates are already on master, so every PR is affected as the new image rolls out.

Change

• openidm-workflow-activiti/pom.xml: drop the second jackson-core declaration.
• openidm-maintenance/pom.xml: drop the repeated org.osgi.util.promise / org.osgi.util.function pair.

Each removed block is an exact copy of an earlier declaration (same scope), so the resolved dependency set of both modules is unchanged.

Verification (Maven 3.10.0)

• master POMs of both modules fail mvn validate with the errors above.
• With this change mvn validate passes for the whole reactor, and mvn -pl openidm-maintenance,openidm-workflow-activiti -am install -DskipTests succeeds.