mtdswap: kill strict error handling option

As Artem Bityutskiy suggested: this option is controversial, as we
do not really have any prove it is useful. And it is too much to have
it as a config parameter. So, better kill it and let the real mtdswap
users decide whether it is needed or not.

Signed-off-by: Yang <Ruirui&lt;ruirui.r.yang@tieto.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>