feat: removes expectation api for a plugin

src/Support/Extendable.php

@@ -1,33 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Pest\Support;
-
-use Closure;
-
-final class Extendable
-{
-    /**
-     * The extendable class.
-     *
-     * @var string
-     */
-    private $extendableClass;
-
-    /**
-     * Creates a new extendable instance.
-     */
-    public function __construct(string $extendableClass)
-    {
-        $this->extendableClass = $extendableClass;
-    }
-
-    /**
-     * Register a custom extend.
-     */
-    public function extend(string $name, Closure $extend): void
-    {
-        $this->extendableClass::extend($name, $extend);
-    }
-}