Simplify test bootstrap by using dev autoloader

This is already being done in other repos of the organisation, let's
make it more consistent then =)

Author: lcobucci

composer.json

@@ -17,5 +17,10 @@
         "psr-4": {
             "React\\EventLoop\\": "src"
         }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "React\\Tests\\EventLoop\\": "tests"
+        }
     }
 }

tests/bootstrap.php

@@ -1,11 +1,5 @@
 <?php
 
-$loader = @include __DIR__ . '/../vendor/autoload.php';
-if (!$loader) {
-    $loader = require __DIR__ . '/../../../../vendor/autoload.php';
-}
-$loader->addPsr4('React\\Tests\\EventLoop\\', __DIR__);
-
 if (!defined('SIGUSR1')) {
     define('SIGUSR1', 1);
 }