Remove RelatedHistogramSet.

docs/histogram-set-json-format.md

Index: docs/histogram-set-json-format.md
diff --git a/docs/histogram-set-json-format.md b/docs/histogram-set-json-format.md
index be9bc5b6330f7b7b4fb8727d9698eb36e0da1994..c5b194b485f6326fca6310207e8691485065f5c0 100644
--- a/docs/histogram-set-json-format.md
+++ b/docs/histogram-set-json-format.md
@@ -129,7 +129,6 @@ The only field that is required for all Diagnostics, `type`, must be one of
  * `GenericSet`
  * `RelatedEventSet`
  * `Breakdown`
- * `RelatedHistogramSet`
  * `RelatedHistogramMap`
  * `RelatedHistogramBreakdown`
  * `TelemetryInfo`
@@ -190,13 +189,6 @@ categories.
  * `values`: required dictionary mapping from a string category name to number values
  * `colorScheme`: optional string specifying how the bar chart should be colored
 
-### RelatedHistogramSet
-
-This allows metrics to annotate which Histograms are related to other
-Histograms.
-
- * `guids`: list of guids of related Histograms
-
 ### RelatedHistogramMap
 
 This allows metrics to annotate which Histograms are related to other