Remove extension executables

Relates to elastic/x-pack-elasticsearch#3734

Original commit: elastic/x-pack-elasticsearch@da75402bc9

plugin/security/src/main/bin/extension

@@ -1,18 +0,0 @@
-#!/bin/bash
-
-# Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
-# or more contributor license agreements. Licensed under the Elastic License;
-# you may not use this file except in compliance with the Elastic License.
-
-source "`dirname "$0"`"/../elasticsearch-env
-
-source "`dirname "$0"`"/x-pack-security-env
-
-exec \
-  "$JAVA" \
-  $ES_JAVA_OPTS \
-  -Des.path.home="$ES_HOME" \
-  -Des.path.conf="$ES_PATH_CONF" \
-  -cp "$ES_CLASSPATH" \
-  org.elasticsearch.xpack.core.extensions.XPackExtensionCli \
-  "$@"