staging: erofs: kill CONFIG_EROFS_FS_IO_MAX_RETRIES

CONFIG_EROFS_FS_IO_MAX_RETRIES seems a runtime setting
and users have no idea about the change in behaviour.

Let's remove the setting currently and could turn it
into a module parameter if it's really needed.

Suggested-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Link: https://lore.kernel.org/r/20190731155752.210602-9-gaoxiang25@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>