staging: lustre: Remove unused memhog functionality

Remove IOC_LIBCFS_MEMHOG ioctl functionality as it is no longer needed thereby
making functions like - kportal_memhog_alloc(), kportal_memhog_free() and type -
struct libcfs_device_userstate unused.

Signed-off-by: Niranjan Dighe <ndighe@visteon.com>
Acked-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>