ubifs, xattr: remove misguided quota flags

Originally, Yang Dongsheng added quota support
for ubifs, but it turned out upstream won't accept it.

Since ubifs don't touch any quota code, S_NOQUOTA flag
is misguided here, and currently it is mainly used to
avoid recursion for system quota files.

Let's make things clearly and remove unnecessary and
misguied quota flags here.

Reported-by: Rock Lee <rockdotlee@gmail.com>
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Signed-off-by: Richard Weinberger <richard@nod.at>