LibC+AK: Remove our custom macros from <assert.h>

Other software might not expect these to be defined and behave
differently if they _are_ defined, e.g. scummvm which checks if
the TODO macro is defined and fails to build if it is.

Userland/Libraries/LibC/pthread_forward.cpp

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <LibC/assert.h>
+#include <AK/Assertions.h>
 #include <LibC/bits/pthread_forward.h>
 
 static PthreadFunctions s_pthread_functions;