1. remove unused function `MoveIssueAcrossProjectBoards`
2. extract the project board condition into a function
3. use db.NoCondition instead of -1. (BTW, the usage of db.NoCondition
is too confusing. Is there any way to avoid that?)
4. remove the unnecessary comment since the ctx refactor is completed.
5. Change `b.ID != 0` to `b.ID > 0`. It's more intuitive but I think
they're the same since board ID can't be negative.
eb1478791f