xwiki-platform-tree-test-pageobjects should only be activated with integration-tests maven profile

xwiki-platform-tree-test-page-objects depends on xwiki-platform-test-ui but this one is only build when the Maven profile "integration-tests" is used, while tree-test-page-objects is build without any specific profile. It might lead to inconsistency: we should build tree-test-pageobjects only if the profile integration-tests is used.