staging/lustre: remove lu_context_keys_dump and lu_debugging_setup

There are no callers of them. Besides, lu_context_keys_dump breaks
build when CONFIG_MODULES is not set.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>