Remove GCE tests files (#5459)

.gitlab-ci.yml

.gitlab-ci/gce.yml

tests/files/gce_centos-weave-kubeadm-sep.yml

tests/files/gce_centos7-calico-ha.yml

tests/files/gce_centos7-flannel-addons.yml

tests/files/gce_centos7-kube-router.yml

tests/files/gce_centos7-multus-calico.yml

tests/files/gce_coreos-alpha-weave-ha.yml

tests/files/gce_coreos-calico-aio.yml

tests/files/gce_coreos-canal.yml

tests/files/gce_coreos-cilium.yml

tests/files/gce_coreos-kube-router.yml

tests/files/gce_debian9-calico-upgrade.yml

tests/files/gce_opensuse-canal.yml

tests/files/gce_oracle-canal.yml

tests/files/gce_rhel7-canal-sep.yml

tests/files/gce_rhel7-weave.yml

tests/files/gce_ubuntu-canal-ha.yml

tests/files/gce_ubuntu-canal-kubeadm.yml

tests/files/gce_ubuntu-contiv-sep.yml