reiserfs: balance_leaf refactor, split up balance_leaf_when_delete

Splut up balance_leaf_when_delete into:
balance_leaf_when_delete_del
balance_leaf_when_cut
balance_leaf_when_delete_left

Also reformat to adhere to CodingStyle.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>