i965: fix new gcc6 warnings

i965: fix new gcc6 warnings

src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp:244:1: warning:
‘void {anonymous}::fs_copy_prop_dataflow::dump_block_data() const’ defined but not used [-Wunused-function]
 fs_copy_prop_dataflow::dump_block_data() const
 ^~~~~~~~~~~~~~~~~~~~~

From looking at git history, it looks like this is intended to be unused
(ie. just for adding on-demand debug prints)

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>