[Docs] Remove Swift plugin on 5.X banches (elastic#34633)

Swift plugin is not (and will not) be available on ES 5.X versions (see: BigDataBoutique/elasticsearch-repository-swift#3 (comment))

Author: john-scalingo

docs/plugins/repository.asciidoc

@@ -26,15 +26,6 @@ The Hadoop HDFS Repository plugin adds support for using HDFS as a repository.
 
 The GCS repository plugin adds support for using Google Cloud Storage service as a repository.
 
-
-[float]
-=== Community contributed repository plugins
-
-The following plugin has been contributed by our community:
-
-* https://github.com/wikimedia/search-repository-swift[Openstack Swift] (by Wikimedia Foundation)
-
-
 include::repository-azure.asciidoc[]
 
 include::repository-s3.asciidoc[]