staging/lustre: remove unused time handling functions

A bunch of API functions deal with time values but are now
completely unused in lustre. This removes them in order to
remove all references to time_t from the header files.

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