First of what version of Hoster are you using ?
Normally all the imported CDG files go in a folder named KMA. and that is where they would normally have stored unless you selected somewhere else.
Now when you imported these other file types did you select a different folders for them?
If you imported all these other files as KMA types as well and in the same folder then the only way I can see to find and delete them is from the edit dialog.
Open edit, select multiple & highlight Book id,enter the wild card * and press find. Look along the top header bar till you come to "Type" and double click it this will sort that column into the different types. All the imported CDG+G will show as "CDCDG" anything else will be the other types, if you want to delete the other types then use shift select to select them then delete them.
But once you do this with KMA types they are gone forever
so don't select the wrong ones.
If on the other hand you imported the others as KMH types it will only remove the files from Hosters database and not delete the original files from the hard drive.
Option 2
If you imported them in to different folder to the folder you imported your CDG disc's, just remove the other folders from the imported files list that is shown on the build database dialog.