Can I remove all missing songs without having to do it one at a time?
Here's a work-around I found:


Create a playlist in iTunes and call it whatever you want (I called
mine "existing songs").
Go to your "All Songs" view, select your entire library, and drag it into the "existing songs" playlist. iTunes will not add missing songs to this playlist, which means "existing songs" will only include songs without an exclamation point.
Create a new smart playlist with the rule "Playlist is not
existing songs". Name it whatever you want (like "Exclamation").
Your new smart playlist will contain only the missing songs, you can re-download them or delete them as you wish.


Source: LifeHacker