Remove an unused variable from AgentClient.cc.
Remove an unused variable from AgentClient.cc.

traff/winpty,rprichard/winpty,fracting/winpty,fracting/winpty,fracting/winpty,dscho/winpty,dscho/winpty,dscho/winpty,peters/winpty,peters/winpty,peters/winpty,dscho/winpty,traff/winpty,rprichard/winpty,rprichard/winpty,fracting/winpty,rprichard/winpty,peters/winpty,traff/winpty,traff/winpty