you can't get rid of a scar, no one can choose to get rid of one short of replacing the entire limb its on.
Yeah, the movies didnt say anything about Ironhide's facial scarring either. Probably a mean looking wound form one of his countless battles, I'm guessing it will be the same for Lockdown.
It's interesting a lot of past transformers also had scars most noticeably Ironhide and shockwave and now lockdown.
do u not see the scar on Shockwave's mouth, i have seen a couple decepticons with scars on them so it isnt a suprise that bay probably just put it in there for the "menacing" look he is giving lockdown