While this is useful for tests, we should really be avoiding it
in 'proper' code as it suffers from TOCTOU issues. Since it is
unused, let's just remove it.
This is a remnant from SerenityOS. Let's avoid confusion as to why we
negate errno when we call Error::from_syscall just to negate it again
when we store the error code.
Before this commit, LibCore/System.h exposed only part of
System::stat API on Windows. Namely, users of Core::System::stat
had to #include <dirent.h> in order to check the return value of stat.
It is OK for low-level libs like LibCore/LibFileSystem, but
S_ISDIR is also used in LibWeb\Loader\GeneratedPagesLoader.cpp.
We want to avoid platform #ifdefs in LibWeb.
