mISDN: Remove obsolete PIPELINE_DEBUG debugging information

stable inclusion
from stable-v5.10.106
commit f97ad179d12ff6789118cf3de3e0236075c5f48b
bugzilla: https://gitee.com/openeuler/kernel/issues/I573US

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f97ad179d12ff6789118cf3de3e0236075c5f48b



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[ Upstream commit 2682ea32 ]

As Leon Romanovsky's tips:
The definition of macro PIPELINE_DEBUG is commented more than 10 years ago
and can be seen as a dead code that should be removed.

Suggested-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>