[DOCS] Remove rollup index ref

docs/reference/rollup/rollup-apis.asciidoc

@@ -6,8 +6,8 @@
 ifdef::permanently-unreleased-branch[]
 
 A rollup aggregates an index's time-series data and stores the results in
-another index, called a rollup index. For example, you can roll up hourly data
-into daily or weekly summaries.
+another index. For example, you can roll up hourly data into daily or weekly
+summaries.
 
 * <<rollup-api,Rollup API>>