The ability to remove traps has limited use these days. In a treasure hunting context, it's common to step back and use the telekenisis spell to trigger the trap, or for lazier people, to simply trigger the trap by hand and absorb the damage. NPC trainers will not train you unless you have at least 50 lockpicking or detect hidden skill.
There are still situations in which the remove trap skill can be useful. If you are hidden/stealthed and want to keep things quiet, it's better to remove a trap than to trigger it. Also, the remove trap skill can be used to remove faction traps set in towns.
Remove trap can be trained by removing traps set using the magic trap spell, but only up to a level of about 60-70. After that it must be trained with either tinker traps or traps on dungeon chests.