Fix broken fsys_getppid()

In particular fsys_getppid always returns the ppid in the initial pid
namespace so it does not work for a process in a pid namespace.

Fix from Eric Biederman just removes the fast system call path.
While it is a little bit sad to see another one of these bite
the dust ... I can't imagine that getppid() is really on any
real applications critical path.

Signed-off-by: Tony Luck <tony.luck@intel.com>