Tests: Remove unused Kernel/ include

This include was unused when it was added in #6993, probably
copy-pasta from Tests/LibC/TestLibCInodeWatcher.cpp where it is
used.

No behavior change.

Tests/LibCore/TestLibCoreFileWatcher.cpp

@@ -4,7 +4,6 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <Kernel/API/InodeWatcherEvent.h>
 #include <LibCore/EventLoop.h>
 #include <LibCore/FileWatcher.h>
 #include <LibCore/Timer.h>