Decompressors: get rid of set_error_fn() macro

Decompressors: get rid of set_error_fn() macro

From: Lasse Collin <lasse.collin@tukaani.org>

set_error_fn() is a useless complication. Only unlzma.c had some use
for it and that was easy to change too.

This also gets rid of the static function pointer "error".

Signed-off-by: Lasse Collin <lasse.collin@tukaani.org>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
Committed-by: Jan Beulich <jbeulich@suse.com>