Removed 3 unnecessary stubbings from KubernetesEngineBuilderClusterTest.java

[ARUS2023]

Testing done

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In our analysis of the project, we observed that

1. 2 unnecessary stubbings which stubbed containerClient method and listAllClusters method in setUpClusterDescriptor are created but are never executed by the test KubernetesEngineBuilderClusterTest.testDoCheckClusterMessageWithEmptyProjectId;
2. 3 unnecessary stubbings which stubbed getClientFactory method, containerClient method and listAllClusters method in setUpClusterDescriptor are created but are never executed by 3 tests KubernetesEngineBuilderClusterTest.testDoFillClusterItemsEmptyWithEmptyCredentialsId, KubernetesEngineBuilderClusterTest.testDoFillClusterItemsEmptyWithEmptyProjectId,KubernetesEngineBuilderClusterTest.testDoCheckClusterMessageWithEmptyCredentialsId.

Unnecessary stubbings are stubbed method calls that were never realized during test execution. Mockito recommends to remove unnecessary stubbings (https://www.javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/exceptions/misusing/UnnecessaryStubbingException.html).

We propose below a solution to remove the unnecessary stubbings.