Remove xrefs to deleted files to fix build

Author: Bob Furu

logging/cluster-logging-release-notes.adoc

@@ -160,8 +160,8 @@ Deprecated functionality is still included in OpenShift Logging and continues to
 
 From {product-title} 4.6 to the present, forwarding logs by using the following legacy methods have been deprecated and will be removed in a future release:
 
-* xref:../logging/cluster-logging-external.adoc#cluster-logging-collector-legacy-fluentd_cluster-logging-external[Forwarding logs using the legacy Fluentd method]
-* xref:../logging/cluster-logging-external.adoc#cluster-logging-collector-legacy-syslog_cluster-logging-external[Forwarding logs using the legacy syslog method]
+* Forwarding logs using the legacy Fluentd method
+* Forwarding logs using the legacy syslog method
 
 Instead, use the following non-legacy methods: