[JENKINS-62477] Remove subversion from suggested

subversion plugin is not actively maintained, however it is in the list
of suggested plugins during first install. Having a unmaintained plugin
in the suggested list of plugins does not look correct.

core/src/main/resources/jenkins/install/platform-plugins.json

@@ -68,7 +68,7 @@
             { "name": "gitlab-plugin" },
             { "name": "p4" },
             { "name": "repo" },
-            { "name": "subversion", "suggested": true },
+            { "name": "subversion" },
             { "name": "tfs" }
         ]
     },