Delete redundant content of 'docs/extend/plugins.md'

Signed-off-by: Yanqiang Miao <miao.yanqiang@zte.com.cn>

Update plugins.md

Update plugins.md

(cherry picked from commit cfe9d2ff1eded7e9bb9b798e780a251c6fc26ef9)
Signed-off-by: Tibor Vass <tibor@docker.com>

docs/extend/plugins.md

@@ -34,7 +34,7 @@ Follow the instructions in the plugin's documentation.
 The sections below provide an inexhaustive overview of available plugins.
 
 <style>
-#content tr td:first-child { white-space: nowrap;}
+#DocumentationText  tr td:first-child { white-space: nowrap;}
 </style>
 
 ### Network plugins