I don't think it's possible to truly remove. However, it should be possible to disguise it.
You can set the attack damage benefit from the primary attribute to 0 in the Gameplay Constants, and you can change the attribute icons and the string Text - General - |cffffff00Primary Attribute|r to something else in Game Interface.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.