[connector, exporter/datadog] Update readme (open-telemetry#34821)

**Description:**
1. `connector.datadogconnector.performance` has already been removed
2. `exporter.datadogexporter.UseLogsAgentExporter` is now enabled by
default so the log service is properly populated by default.

connector/datadogconnector/README.md

@@ -181,10 +181,3 @@ connectors:
         #
         # bucket_interval: 30s
 ```
-
-**NOTE**: `compute_stats_by_span_kind` and `peer_tags_aggregation` only work when the feature gate `connector.datadogconnector.performance` is enabled. See below for details on this feature gate.
-
-## Feature Gate for Performance
-
-In case you are experiencing high memory usage with Datadog Connector, similar to [issue](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/29755), use the feature gate `connector.datadogconnector.performance`. With the feature gate enabled, Datadog Connector takes OTLP traces and produces OTLP metric with the name `dd.internal.stats.payload`. This Metric has an attribute `dd.internal.stats.payload` that contains the bytes for StatsPayload. With the feature gate, we can use Datadog Connector only in conjunction with Datadog Exporter. Please enable the feature only if needed for performance reasons and higher throughput. Enable the feature gate on all collectors (especially in gateway deployment) in the pipeline that sends data to Datadog. We plan to refactor this component in the future so that the signals produced are usable in any metrics pipeline.
-

exporter/datadogexporter/README.md

@@ -62,7 +62,9 @@ Note that we are currently migrating the Datadog metrics exporter to use the met
 
 ### Remap OTel’s service.name attribute to service for logs
 
-For Datadog Exporter versions 0.83.0 and later, the `service` field of OTel logs is populated as [OTel semantic convention](https://opentelemetry.io/docs/specs/semconv/resource/#service) `service.name`. However, `service.name` is not one of the default [service attributes](https://docs.datadoghq.com/logs/log_configuration/pipelines/?tab=service#service-attribute) in Datadog’s log preprocessing.
+**NOTE** this workaround is only needed when feature gate `exporter.datadogexporter.UseLogsAgentExporter` is disabled. This feature gate is enabled by default starting v0.108.0.
+
+For Datadog Exporter versions 0.83.0 - v0.107.0, the `service` field of OTel logs is populated as [OTel semantic convention](https://opentelemetry.io/docs/specs/semconv/resource/#service) `service.name`. However, `service.name` is not one of the default [service attributes](https://docs.datadoghq.com/logs/log_configuration/pipelines/?tab=service#service-attribute) in Datadog’s log preprocessing.
 
 To get the service field correctly populated in your logs, you can specify service.name to be the source of a log’s service by setting a [log service remapper processor](https://docs.datadoghq.com/logs/log_configuration/pipelines/?tab=service#service-attribute).