fix(ci): remove duplicate geaflow-cluster dependency in geaflow-mcp pom

[E2ern1ty]

What changes were proposed in this pull request?

Removes the second, byte-identical declaration of the geaflow-cluster dependency in geaflow-mcp/pom.xml (it was declared at lines 125 and 135 with the same groupId/artifactId/version and no differing scope or exclusions).

Why it matters — CI is red for every open PR

Newer Maven builds (as currently preinstalled on the ubuntu-latest runner image) turn duplicate dependency declarations from a warning into a model-validation error, failing the whole reactor before any compile:

[ERROR] The project org.apache.geaflow:geaflow-mcp:0.8.0-SNAPSHOT has 1 error
[ERROR]   'dependencies.dependency.(groupId:artifactId:type:classifier)' must be unique:
        org.apache.geaflow:geaflow-cluster:jar -> duplicate declaration of version ${project.version} @ line 133, column 21

This is environment drift exposing a pre-existing problem, not a regression from any recent PR: the duplicate has been in the file for a while, and master's last green build (Sep 14) predates the runner image update. Currently every PR against master fails CI within ~25s — e.g. #876, #877, #878.

Verified locally that the full reactor (mvn validate -Pjdk8 with the same module exclusion as CI) passes after the removal.

How was this PR tested?

• mvn -B validate -Pjdk8 -pl '!geaflow/geaflow-plugins/geaflow-store/geaflow-store-vector' — full reactor model builds cleanly.
• The deleted block is byte-identical to the retained one (no scope/exclusion loss).
• Production environment verified