Remove cloudevent metrics from documentation

CloudEvent metrics was removed as part of pr #6827 . We removed this
from documentation also.

docs/metrics.md

@@ -23,7 +23,6 @@ We expose several kinds of exporters, including Prometheus, Google Stackdriver,
 | `tekton_pipelines_controller_running_taskruns_throttled_by_quota_count` | Gauge | | experimental |
 | `tekton_pipelines_controller_running_taskruns_throttled_by_node_count`  | Gauge | | experimental |
 | `tekton_pipelines_controller_taskruns_pod_latency` | Gauge | `namespace`=&lt;taskruns-namespace&gt; <br> `pod`= &lt; taskrun_pod_name&gt; <br> `*task`=&lt;task_name&gt; <br> `*taskrun`=&lt;taskrun_name&gt;<br> | experimental |
-| `tekton_pipelines_controller_cloudevent_count` | Counter | `*pipeline`=&lt;pipeline_name&gt; <br> `*pipelinerun`=&lt;pipelinerun_name&gt; <br> `status`=&lt;status&gt; <br> `*task`=&lt;task_name&gt; <br> `*taskrun`=&lt;taskrun_name&gt;<br> `namespace`=&lt;pipelineruns-taskruns-namespace&gt;| experimental |
 | `tekton_pipelines_controller_client_latency_[bucket, sum, count]` | Histogram | | experimental |
 
 The Labels/Tag marked as "*" are optional. And there's a choice between Histogram and LastValue(Gauge) for pipelinerun and taskrun duration metrics.
@@ -55,7 +54,7 @@ Following values are available in the configmap:
 | metrics.pipelinerun.duration-type | `histogram` | `tekton_pipelines_controller_pipelinerun_duration_seconds` is of type histogram |
 | metrics.pipelinerun.duration-type | `lastvalue` | `tekton_pipelines_controller_pipelinerun_duration_seconds` is of type gauge or lastvalue |
 
-Histogram value isn't available when pipelinerun or taskrun labels are selected. The Lastvalue or Gauge will be provided. It serves no purpose because we will get only bar in a histogram. Also, setting `*-run` level metrics aren't recommended because they lead to unbounded cardinality which degrades observability database.
+Histogram value isn't available when pipelinerun or taskrun labels are selected. The Lastvalue or Gauge will be provided. Histogram would serve no purpose because it would generate a single bar. TaskRun and PipelineRun level metrics aren't recommended because they lead to an unbounded cardinality which degrades the observability database.
 
 To check that appropriate values have been applied in response to configmap changes, use the following commands:
 ```shell