[2.x] Remove old LegacyTestResponse

Author: nshiro

src/ServiceProvider.php

@@ -2,7 +2,6 @@
 
 namespace Inertia;
 
-use Illuminate\Foundation\Testing\TestResponse as LegacyTestResponse;
 use Illuminate\Http\Request;
 use Illuminate\Routing\Router;
 use Illuminate\Support\ServiceProvider as BaseServiceProvider;
@@ -99,13 +98,6 @@ protected function registerTestingMacros(): void
             return;
         }
 
-        // Laravel <= 6.0
-        if (class_exists(LegacyTestResponse::class)) {
-            LegacyTestResponse::mixin(new TestResponseMacros);
-
-            return;
-        }
-
         throw new LogicException('Could not detect TestResponse class.');
     }