staging/lustre/libcfs: remove upcall cache

The upcall cache is unused so remove include/linux/libcfs/lucache.h
and lustre/libcfs/upcall_cache.c.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>