updated versioned plugin docs (#1808)

Author: github-actions[bot]

docs/versioned-plugins/inputs/beats-index.asciidoc

@@ -103,10 +103,6 @@ include::{include_path}/version-list-intro.asciidoc[]
 | <<v3.1.23-plugins-inputs-beats,v3.1.23>> | 2017-07-12
 | <<v3.1.22-plugins-inputs-beats,v3.1.22>> | 2017-07-12
 | <<v3.1.21-plugins-inputs-beats,v3.1.21>> | 2017-06-23
-| <<v3.1.20-plugins-inputs-beats,v3.1.20>> | 2017-06-23
-| <<v3.1.19-plugins-inputs-beats,v3.1.19>> | 2017-06-22
-| <<v3.1.18-plugins-inputs-beats,v3.1.18>> | 2017-06-07
-| <<v3.1.17-plugins-inputs-beats,v3.1.17>> | 2017-06-05
 |=======================================================================
 
 include::beats-v7.0.2.asciidoc[]
@@ -207,8 +203,4 @@ include::beats-v3.1.24.asciidoc[]
 include::beats-v3.1.23.asciidoc[]
 include::beats-v3.1.22.asciidoc[]
 include::beats-v3.1.21.asciidoc[]
-include::beats-v3.1.20.asciidoc[]
-include::beats-v3.1.19.asciidoc[]
-include::beats-v3.1.18.asciidoc[]
-include::beats-v3.1.17.asciidoc[]