Revert "iio: add configuration option for debug support"

This reverts commit 98a5e9e9.

IIO, like the rest of the kernel, should rely on dynamic debugging, not
have a special config option for it.  That way, no user has to rebuild
their kernel to have debug messages, which is a good thing, let's not
revert back to the bad old days of the 2000's.

Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>