Get rid of 'if logdebug: logdebug(...)' pattern using a noop function

Suggested by @Mineo in https://github.com/musicbrainz/picard/pull/254/files#r11290500
Merge pull request #280 from zas/i18n_noop

Get rid of 'if logdebug: logdebug(...)' pattern using a noop function