Remove tbarker from codeowners (#23877)

**Description:**
Fixes
#23405

@tbarker25 doesn't work on OpenTelemetry for Google anymore.

cc @punya

.github/CODEOWNERS

@@ -53,8 +53,8 @@ exporter/dynatraceexporter/                              @open-telemetry/collect
 exporter/elasticsearchexporter/                          @open-telemetry/collector-contrib-approvers @JaredTan95
 exporter/f5cloudexporter/                                @open-telemetry/collector-contrib-approvers @gramidt
 exporter/fileexporter/                                   @open-telemetry/collector-contrib-approvers @atingchen
-exporter/googlecloudexporter/                            @open-telemetry/collector-contrib-approvers @aabmass @dashpole @jsuereth @punya @tbarker25 @damemi @psx95
-exporter/googlemanagedprometheusexporter/                @open-telemetry/collector-contrib-approvers @aabmass @dashpole @jsuereth @punya @tbarker25 @damemi @psx95
+exporter/googlecloudexporter/                            @open-telemetry/collector-contrib-approvers @aabmass @dashpole @jsuereth @punya @damemi @psx95
+exporter/googlemanagedprometheusexporter/                @open-telemetry/collector-contrib-approvers @aabmass @dashpole @jsuereth @punya @damemi @psx95
 exporter/googlecloudpubsubexporter/                      @open-telemetry/collector-contrib-approvers @alexvanboxel
 exporter/influxdbexporter/                               @open-telemetry/collector-contrib-approvers @jacobmarble
 exporter/instanaexporter/                                @open-telemetry/collector-contrib-approvers @jpkrohling @hickeyma