Gem::Commands::SetupCommand#remove_old_lib_files

# File tmp/rubies/ruby-3.0.5/lib/rubygems/commands/setup_command.rb, line 526
def remove_old_lib_files(lib_dir)
  lib_dirs = { File.join(lib_dir, 'rubygems') => 'lib/rubygems' }
  lib_dirs[File.join(lib_dir, 'bundler')] = 'bundler/lib/bundler'
  lib_dirs.each do |old_lib_dir, new_lib_dir|
    lib_files = files_in(new_lib_dir)

    old_lib_files = files_in(old_lib_dir)

    to_remove = old_lib_files - lib_files

    gauntlet_rubygems = File.join(lib_dir, 'gauntlet_rubygems.rb')
    to_remove << gauntlet_rubygems if File.exist? gauntlet_rubygems

    to_remove.delete_if do |file|
      file.start_with? 'defaults'
    end

    remove_file_list(to_remove, old_lib_dir)
  end
end