This is pretty much a regression of bug #485708. Simple to reproduce: emerge -C freerdp rdesktop && USE="-rdesktop" emerge -v krdc; Then start krdc and notice RDP is still there, it just fails with the error "could not start freerdp make sure freerdp is properly installed." Im not sure how gentoo wants to handle this. There could be a rdesktop & freerdp use flag. There could be a virtual rdp package, or even a simple check, use rdesktop | freerdp. If no RDP support desired, some patch or configuration option should prevent RDP options in the GUI.
Technically we're not supposed to have that USE flag at all because all it does it pull in a runtime-only dependency. Upstream builds RDP stuff unconditionally on X11, see rdp/CMakeLists.txt. I would suggest raising the issue with them if you would like a new build option provided.
