I use the theme "iPad 3 Tap to Unlock." It comes in two versions, regular and clear. I use the clear version, which removes the camera icon.
This is what it looks like installed on my iPad3 running iOS 6.1.2:
If you don't want to lose the slider, I am sure you can edit the theme so that it's not removed. This works for me - I am sure there are others.
Marilyn
P.S. And yes, those two little lines are a result of not having full compatibility with iOS 6 (notice how the two gray bars are missing from the top and bottom ... well, except for those line). It's fixable - I just haven't gotten around to figuring out how...