bpf, cpumap: Remove unused cmap field from bpf_cpu_map_entry

Since commit cdfafe98 ("xdp: Make cpumap flush_list common for all
map instances"), cmap is no longer used, so just remove it.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230728014942.892272-2-houtao@huaweicloud.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>