staging: lustre: discard lu_buf allocation library.

This library code is unnecessarily generic, but also
not generic enough.  Library code that performs
allocations should always take a gfp_flags argument.

So discard the library and in the one file where it is used,
just use kzalloc or krealloc as needed.
In this context, it is clear that vmalloc is never needed.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>