btrfs: remove unused Opt enums

The following three Opt_* enums haven't been utilized since the port to
new mount API:

- Opt_ignorebadroots
- Opt_ignoredatacsums
- Opt_rescue_all

All those enums are from the old day where we have dedicated mount
options, nowadays they have been moved to "rescue=" mount option
groups, and no more global tokens for them.

So we can safely remove them now.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>