misc: echo: Remove

misc: echo: Remove

'echo' is a software echo canceller for telco use, however
it's not used in the kernel at all.

Remove it.

It was moved from staging in 2014 by
commit Fixes: 6e2055a9e56e ("staging: echo: move to drivers/misc/")

Some discussion on lkml:
  https://lore.kernel.org/all/Z7tZhYET41DAoHVf@gallifrey/
with Arnd and Harald, led to the 'dahdi' package which is part of
Asterisk:

  https://gitea.osmocom.org/retronetworking/dahdi-linux

which can build with the 'echo' module, but is normally configured
with out it.
Dahdi is large, old, only lightly maintained and with a big API, so
there's no hope now of ever merging it into the main kernel tree.

Debian do package Dahdi, and in their package they actually include
a copy of the 'echo' module rather than using the kernel from the
upstream kernel.  So even in the few cases where it is packaged
and built, the kernel copy isn't used.

Signed-off-by: "Dr. David Alan Gilbert" <linux@treblig.org>
Link: https://lore.kernel.org/r/20250427224022.113678-1-linux@treblig.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>