Revert "build: Add custom grafana build image with plugins installed"

We are going to upgrade Grafana version to 6.7.4 for a CVE fix, hence
including the piechart-panel plugin by default.
This reverts commit 08825e9, which
isn't needed anymore.
See: #2600

buildchain/buildchain/image.py

@@ -180,6 +180,9 @@ def _operator_image(name: str, **kwargs: Any) -> targets.OperatorImage:
         'kube-scheduler',
         'nginx-ingress-defaultbackend-amd64',
     ],
+    constants.GRAFANA_REPOSITORY: [
+        'grafana',
+    ],
     constants.INGRESS_REPOSITORY: [
         'nginx-ingress-controller',
     ],
@@ -214,10 +217,6 @@ def _operator_image(name: str, **kwargs: Any) -> targets.OperatorImage:
 # }}}
 # Container images to build {{{
 TO_BUILD : Tuple[targets.LocalImage, ...] = (
-    _local_image(
-        name='grafana',
-        build_args={'GRAFANA_IMAGE_VERSION': versions.GRAFANA_IMAGE_VERSION},
-    ),
     _local_image(
         name='salt-master',
         build_args={'SALT_VERSION': versions.SALT_VERSION},

buildchain/buildchain/versions.py

@@ -57,9 +57,8 @@ def load_version_information() -> None:
 CENTOS_BASE_IMAGE_SHA256 : str = \
     '6ae4cddb2b37f889afd576a17a5286b311dcbf10a904409670827f6f9b50065e'
 
-GRAFANA_IMAGE_VERSION : str = '6.4.2'
-NGINX_IMAGE_VERSION   : str = '1.15.8'
-NODEJS_IMAGE_VERSION  : str = '10.16.0'
+NGINX_IMAGE_VERSION  : str = '1.15.8'
+NODEJS_IMAGE_VERSION : str = '10.16.0'
 
 # Current build IDs, to be augmented whenever we rebuild the corresponding
 # image, e.g. because the `Dockerfile` is changed, or one of the dependencies
@@ -107,6 +106,11 @@ def _version_prefix(version: str, prefix: str = 'v') -> str:
         version='3.3.10',
         digest='sha256:17da501f5d2a675be46040422a27b7cc21b8a43895ac998b171db1c346f361f7',
     ),
+    Image(
+        name='grafana',
+        version='6.4.2',
+        digest='sha256:8c2238eea9d3d39aeb6174db2e30b233fd2546128ec1fa1bc64f8058afd51e68',
+    ),
     Image(
         name='k8s-sidecar',
         version='0.1.20',
@@ -183,11 +187,6 @@ def _version_prefix(version: str, prefix: str = 'v') -> str:
         digest='sha256:c0bcb231fe67cd11fd26f7adf5ac1080dfac189ac94705538bd4ab7dd99a98a9',
     ),
     # Local images
-    Image(
-        name='grafana',
-        version=GRAFANA_IMAGE_VERSION,
-        digest=None,
-    ),
     Image(
         name='metalk8s-ui',
         version=VERSION,