staging: erofs: remove redundant CONFIG_EROFS_FS_XATTRs

some CONFIG_EROFS_FS_XATTR conditions were added because of
the historial Linux kernel compatibility, which are unneeded now.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>