TIE Advanced target lock

His special does not inflict target lock. His basic does. What you are seeing under his special is what that ability will do if the target already has target lock. It is the same with a lot of other ships description. If they seperate a section with yellow letters that say Target Lock then that is something extra that ability does when an enemy already has TL. So his special will not dispell the taunt unless you already have applied TL to HT.

Also be aware that if any enemy has breach and HT loses taunt he will regain taunt for one turn. So if you use Vader's special on a target locked HT and one of your ships have breach he will immediately gain taunt for 1 more turn. If you run your battles on 4x speed this happens so fast you may think nothing happened.