Findadv: Convert some messages from LYXERR0(...) to LYXERR(Debug::INFO, ...)

Findadv: Convert some messages from LYXERR0(...) to LYXERR(Debug::INFO, ...)

Due to a hint from Scott:
> I don't think it should be printed to LYXERR0. That goes to the terminal
> for the user. Even our lyx2lyx tests fail if they detect any information
> printed to the terminal (although we escape some warnings). If "find" is
> not a good debug level for it, maybe we can put it in "info" (the first
> debug level)?