Show only imported files in iTunes
You can delete items whose files have been removed by running this from AppleScript Editor:

tell application "iTunes"
    repeat 5 times
        repeat with t in file tracks of library playlist 1
            try
                if location of t is missing value then delete t
            end try
        end repeat
    end repeat
end tell


I don't know why you have to run it multiple times, but it usually removes all items after about five times.