Remove dependency:bundler task (#13146)

Already done on master in #12017, this is unnecessary as it is already being done
by installBundler.

rakelib/dependency.rake

@@ -1,22 +0,0 @@
-# Licensed to Elasticsearch B.V. under one or more contributor
-# license agreements. See the NOTICE file distributed with
-# this work for additional information regarding copyright
-# ownership. Elasticsearch B.V. licenses this file to you under
-# the Apache License, Version 2.0 (the "License"); you may
-# not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#  http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing,
-# software distributed under the License is distributed on an
-# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
-# KIND, either express or implied.  See the License for the
-# specific language governing permissions and limitations
-# under the License.
-
-namespace "dependency" do
-  task "bundler" do
-    Rake::Task["gem:require"].invoke("bundler", "~> 1.17.3")
-  end
-end # namespace dependency

rakelib/vendor.rake

@@ -31,8 +31,6 @@ namespace "vendor" do
   task "gems", [:bundle] do |task, args|
     require "bootstrap/environment"
 
-    Rake::Task["dependency:bundler"].invoke
-
     puts("Invoking bundler install...")
     output, exception = LogStash::Bundler.invoke!(:install => true)
     puts(output)