Remove top-level size from ReindexRequest (#5471)

This was removed from ES in 8.0.0 (see
elastic/elasticsearch#43373).

(cherry picked from commit 263280a)

Author: PeteGillinElastic

output/openapi/elasticsearch-openapi.json

@@ -176,7 +176,6 @@ export interface Request extends RequestBase {
      * The script to run to update the document source or metadata when reindexing.
      */
     script?: Script
-    size?: long
     /**
      * The source you are copying from.
      */