Usage help shows duplicate aliases if registered with same alias multiple times

[remkop]

Example:

TopLevelCommand top = new TopLevelCommand();
SubCommandWithAlias sub = new SubCommandWithAlias();
CommandLine cmd = new CommandLine(top).addSubcommand("task", sub, "t", "t");
cmd.usage(System.out);

Prints:

Usage: cb [COMMAND]
Commands:
  task, t, t, t  subcommand with alias

But expected the duplicate aliases to be filtered (deduplicated):

Usage: cb [COMMAND]
Commands:
  task, t  subcommand with alias