Remove OpenLab CI from README as it's EOL.
Thanks OpenLab for providing ARM regression tests service for a very
long time.
**Concourse Pipeline** [![Concourse Build Status](https://prod.ci.gpdb.pivotal.io/api/v1/teams/main/pipelines/gpdb_master/badge)](https://prod.ci.gpdb.pivotal.io/teams/main/pipelines/gpdb_master) |
**Travis Build** [![Travis Build Status](https://travis-ci.org/greenplum-db/gpdb.svg?branch=master)](https://travis-ci.org/greenplum-db/gpdb) |
-**Zuul Regression Test On Arm** [![Zuul Regression Test Status](http://openlabtesting.org:15000/badge?project=greenplum-db%2Fgpdb)](https://status.openlabtesting.org/builds/builds?project=greenplum-db%2Fgpdb&job_name=gpdb-installcheck-world-tests-on-arm64)
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