[taas] Use ubuntu minimal as advanced image

Other scenario jobs already using ubuntu minimal as
advanced image and works fine, let's also use in taas
scenario jobs.

The minimal image takes less resources and boot
faster compared to regular image.

Change-Id: I83ec778609a4c2fdaf9411a41c541b0fc32b6648
diff --git a/zuul.d/master_jobs.yaml b/zuul.d/master_jobs.yaml
index 48b146d..c04111f 100644
--- a/zuul.d/master_jobs.yaml
+++ b/zuul.d/master_jobs.yaml
@@ -1297,11 +1297,6 @@
         - taas-vlan-filter
       devstack_localrc:
         NETWORK_API_EXTENSIONS: "{{ (network_api_extensions_common + network_api_extensions_tempest) | join(',') }}"
-        IMAGE_URLS: https://cloud-images.ubuntu.com/releases/bionic/release/ubuntu-18.04-server-cloudimg-amd64.img
-        ADVANCED_IMAGE_NAME: ubuntu-18.04-server-cloudimg-amd64
-        ADVANCED_INSTANCE_TYPE: ntp_image_384M
-        ADVANCED_INSTANCE_USER: ubuntu
-        CUSTOMIZE_IMAGE: false
         BUILD_TIMEOUT: 784
         Q_AGENT: openvswitch
         Q_ML2_TENANT_NETWORK_TYPE: vxlan,vlan