You can either move a song in a playlist to the trash or remove it (it remains in your song list). Search in Help for the different ways of doing this for your device.

The trailing numbers in a song’s title in Trash happens when a song is moved into trash, where a song with the same title is already there. (It keeps them distinct in case you need to sort through them to restore a specific one.)

If you restore from trash, the song (or all songs listing in trash) are moved back into your Songs list. For restore all, you could always do screenshots of the songs in the trash first, so you can check them after restoring (hint, use Find).
(Users might like to check and empty Trash from time to time, so if a song needs restoring, it is easier to find with less songs in.)

Once the trash is emptied or a song is deleted from trash, you cannot get them back without going to your backups, Time machine (Mac) or another of your devices which has it.
If you use iCloud sync, another of your (Apple) devices might still have a deleted song (depending on when it did a sync last).
Turn on Airplane mode before opening iReal Pro (otherwise it will start a sync), perhaps turn off iCloud sync in iReal Pro, prepare sending the deleted song(s) via email to yourself, then turn off Airplane mode again for it to send, and import again on your original device.