aufs: tiny, headers after fs_context

commit ac38cd415fb9089b0c4ccb8f1d0588da9d6e14e5 aufs5-standalone upstream.

Since new opts.h includes linux/namei.h, all other source files are
not necessary to include it anymore.

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>