Remove interfaceRegister from libvirt_private.syms

This symbol is conditional, it would need to be exported conditional to
work properly with MinGW. So just remove it, as no other driver register
function is listed in the symbols files.

src/libvirt_private.syms

@@ -257,10 +257,6 @@ virInterfaceObjUnlock;
 virInterfaceObjListFree;
 
 
-# interface_driver.h
-interfaceRegister;
-
-
 # iptables.h
 iptablesAddForwardAllowCross;
 iptablesAddForwardAllowIn;