php: remove unused file

src/php/tests/interop/message_set.php

@@ -1,26 +0,0 @@
-<?php
-// DO NOT EDIT! Generated by Protobuf-PHP protoc plugin 1.0
-// Source: net/proto2/bridge/proto/message_set.proto
-//   Date: 2014-12-03 22:02:20
-
-namespace proto2\bridge {
-
-  class MessageSet extends \DrSlump\Protobuf\Message {
-
-
-    /** @var \Closure[] */
-    protected static $__extensions = array();
-
-    public static function descriptor()
-    {
-      $descriptor = new \DrSlump\Protobuf\Descriptor(__CLASS__, 'proto2.bridge.MessageSet');
-
-      foreach (self::$__extensions as $cb) {
-        $descriptor->addField($cb(), true);
-      }
-
-      return $descriptor;
-    }
-  }
-}
-