Mark the completion.registerLibraryPaths as deprecated in the Dart Analysis Server.

Change-Id: Ia0b305d9ebaf1a5416994e1fa0959a29d043a87b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/125930
Reviewed-by: Jaime Wren <jwren@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Jaime Wren <jwren@google.com>

pkg/analysis_server/tool/spec/generated/java/AnalysisServer.java

@@ -439,6 +439,8 @@ public interface AnalysisServer {
    *         the client is interested in receiving completion suggestions. If one configured path is
    *         beneath another, the descendent will override the ancestors' configured libraries of
    *         interest.
+   *
+   * @deprecated
    */
   public void completion_registerLibraryPaths(List<LibraryPathSet> paths);