Update search.asciidoc

Removed operation threading from the docs. Not supported since v1.2.0

Closes #9917

docs/java-api/search.asciidoc

@@ -74,24 +74,6 @@ while (true) {
 }
 --------------------------------------------------
 
-
-=== Operation Threading
-
-The search API allows one to set the threading model the operation will be
-performed when the actual execution of the API is performed on the same
-node (the API is executed on a shard that is allocated on the same
-server).
-
-There are three threading modes.The `NO_THREADS` mode means that the
-search operation will be executed on the calling thread. The
-`SINGLE_THREAD` mode means that the search operation will be executed on
-a single different thread for all local shards. The `THREAD_PER_SHARD`
-mode means that the search operation will be executed on a different
-thread for each local shard.
-
-The default mode is `THREAD_PER_SHARD`.
-
-
 [[msearch]]
 === MultiSearch API