pcm: remove unused macros of COPY_LABELS/COPY_END
pcm: remove unused macros of COPY_LABELS/COPY_END

A commit 7b054f4dce56 obsoleted usage of a pair of COPY_LABELS/COPY_END,
however it did not remove some codes in 'src/pcm/plugin_ops.h'.

This commit removes them in a point to reduce the amount of code to
maintain.

Signed-off-by: Takashi Sakamoto <d5ec7d0cd8074757a1f5eb708bc105c3065a65ea@sakamocchi.jp>
Signed-off-by: Takashi Iwai <4596b3305151c7ee743192a95d394341e3d3b644@suse.de>

alsa-project/alsa-lib,tiwai/alsa-lib,takaswie/alsa-lib,tiwai/alsa-lib,alsa-project/alsa-lib,takaswie/alsa-lib,takaswie/alsa-lib,alsa-project/alsa-lib,takaswie/alsa-lib,tiwai/alsa-lib,tiwai/alsa-lib,takaswie/alsa-lib,alsa-project/alsa-lib