staging/lustre: Remove lustre_build_version.h

of the two macroses is contained the LUSTRE_RELEASE was unused and
BUILD_VERSION is too generically named and was replaced with
LUSTRE_VERSION_STRING with all the users (provided by lustre_ver.h)

With in-kernel client the build version should be combined with
kernel build information anyway.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>